| Message ID | 20191112150105.2498-4-robert.foley@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Make the qemu_logfile handle thread safe. | expand |
Robert Foley <robert.foley@linaro.org> writes: > This now allows changing the logfile while logging is active, > and also solves the issue of a seg fault while changing the logfile. > > Any read access to the qemu_logfile handle will use > the rcu_read_lock()/unlock() around the use of the handle. > To fetch the handle we will use atomic_rcu_read(). > We also in many cases do a check for validity of the > logfile handle before using it to deal with the case where the > file is closed and set to NULL. > > The cases where we write to the qemu_logfile will use atomic_rcu_set(). > Writers will also use call_rcu() with a newly added qemu_logfile_free > function for freeing/closing when readers have finished. > > Signed-off-by: Robert Foley <robert.foley@linaro.org> > --- > v1 > - Changes for review comments. > - Minor changes to definition of QemuLogFile. > - Changed qemu_log_separate() to fix unbalanced and > remove qemu_log_enabled() check. > - changed qemu_log_lock() to include else. > - make qemu_logfile_free static. > - use g_assert(logfile) in qemu_logfile_free. > - Relocated unlock out of if/else in qemu_log_close(), and > in qemu_set_log(). > --- > include/qemu/log.h | 42 ++++++++++++++++++++++---- > util/log.c | 73 +++++++++++++++++++++++++++++++++------------- > include/exec/log.h | 33 ++++++++++++++++++--- > tcg/tcg.c | 12 ++++++-- > 4 files changed, 128 insertions(+), 32 deletions(-) > > diff --git a/include/qemu/log.h b/include/qemu/log.h > index a7c5b01571..528e1f9dd7 100644 > --- a/include/qemu/log.h > +++ b/include/qemu/log.h > @@ -3,9 +3,16 @@ > > /* A small part of this API is split into its own header */ > #include "qemu/log-for-trace.h" > +#include "qemu/rcu.h" > + > +typedef struct QemuLogFile { > + struct rcu_head rcu; > + FILE *fd; > +} QemuLogFile; > > /* Private global variable, don't use */ > -extern FILE *qemu_logfile; > +extern QemuLogFile *qemu_logfile; > + > > /* > * The new API: > @@ -25,7 +32,16 @@ static inline bool qemu_log_enabled(void) > */ > static inline bool qemu_log_separate(void) > { > - return qemu_logfile != NULL && qemu_logfile != stderr; > + QemuLogFile *logfile; > + bool res = false; > + > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile && logfile->fd != stderr) { > + res = true; > + } > + rcu_read_unlock(); > + return res; > } > > #define CPU_LOG_TB_OUT_ASM (1 << 0) > @@ -55,14 +71,23 @@ static inline bool qemu_log_separate(void) > > static inline FILE *qemu_log_lock(void) > { > - qemu_flockfile(qemu_logfile); > - return logfile->fd; > + QemuLogFile *logfile; > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + qemu_flockfile(logfile->fd); > + return logfile->fd; > + } else { > + rcu_read_unlock(); > + return NULL; > + } > } > > static inline void qemu_log_unlock(FILE *fd) > { > if (fd) { > qemu_funlockfile(fd); > + rcu_read_unlock(); > } > } > > @@ -73,9 +98,14 @@ static inline void qemu_log_unlock(FILE *fd) > static inline void GCC_FMT_ATTR(1, 0) > qemu_log_vprintf(const char *fmt, va_list va) > { > - if (qemu_logfile) { > - vfprintf(qemu_logfile, fmt, va); > + QemuLogFile *logfile; > + > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + vfprintf(logfile->fd, fmt, va); > } > + rcu_read_unlock(); > } > > /* log only if a bit is set on the current loglevel mask: > diff --git a/util/log.c b/util/log.c > index c25643dc99..802b8de42e 100644 > --- a/util/log.c > +++ b/util/log.c > @@ -28,7 +28,7 @@ > > static char *logfilename; > static QemuMutex qemu_logfile_mutex; > -FILE *qemu_logfile; > +QemuLogFile *qemu_logfile; > int qemu_loglevel; > static int log_append = 0; > static GArray *debug_regions; > @@ -37,10 +37,14 @@ static GArray *debug_regions; > int qemu_log(const char *fmt, ...) > { > int ret = 0; > - if (qemu_logfile) { > + QemuLogFile *logfile; > + > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > va_list ap; > va_start(ap, fmt); > - ret = vfprintf(qemu_logfile, fmt, ap); > + ret = vfprintf(logfile->fd, fmt, ap); > va_end(ap); > > /* Don't pass back error results. */ > @@ -48,6 +52,7 @@ int qemu_log(const char *fmt, ...) > ret = 0; > } > } > + rcu_read_unlock(); > return ret; > } > > @@ -56,11 +61,23 @@ static void __attribute__((__constructor__)) qemu_logfile_init(void) > qemu_mutex_init(&qemu_logfile_mutex); > } > > +static void qemu_logfile_free(QemuLogFile *logfile) > +{ > + g_assert(logfile); > + > + if (logfile->fd != stderr) { > + fclose(logfile->fd); > + } > + g_free(logfile); > +} > + > static bool log_uses_own_buffers; > > /* enable or disable low levels log */ > void qemu_set_log(int log_flags) > { > + QemuLogFile *logfile; > + > qemu_loglevel = log_flags; > #ifdef CONFIG_TRACE_LOG > qemu_loglevel |= LOG_TRACE; > @@ -70,44 +87,50 @@ void qemu_set_log(int log_flags) > qemu_mutex_lock(&qemu_logfile_mutex); > if (!qemu_logfile && > (is_daemonized() ? logfilename != NULL : qemu_loglevel)) { > + logfile = g_new0(QemuLogFile, 1); > if (logfilename) { > - qemu_logfile = fopen(logfilename, log_append ? "a" : "w"); > - if (!qemu_logfile) { > + logfile->fd = fopen(logfilename, log_append ? "a" : "w"); > + if (!logfile->fd) { > + g_free(logfile); > perror(logfilename); > _exit(1); > } > /* In case we are a daemon redirect stderr to logfile */ > if (is_daemonized()) { > - dup2(fileno(qemu_logfile), STDERR_FILENO); > - fclose(qemu_logfile); > + dup2(fileno(logfile->fd), STDERR_FILENO); > + fclose(logfile->fd); > /* This will skip closing logfile in qemu_log_close() */ > - qemu_logfile = stderr; > + logfile->fd = stderr; > } > } else { > /* Default to stderr if no log file specified */ > assert(!is_daemonized()); > - qemu_logfile = stderr; > + logfile->fd = stderr; > } > /* must avoid mmap() usage of glibc by setting a buffer "by hand" */ > if (log_uses_own_buffers) { > static char logfile_buf[4096]; > > - setvbuf(qemu_logfile, logfile_buf, _IOLBF, sizeof(logfile_buf)); > + setvbuf(logfile->fd, logfile_buf, _IOLBF, sizeof(logfile_buf)); > } else { > #if defined(_WIN32) > /* Win32 doesn't support line-buffering, so use unbuffered output. */ > - setvbuf(qemu_logfile, NULL, _IONBF, 0); > + setvbuf(logfile->fd, NULL, _IONBF, 0); > #else > - setvbuf(qemu_logfile, NULL, _IOLBF, 0); > + setvbuf(logfile->fd, NULL, _IOLBF, 0); > #endif > log_append = 1; > } > + atomic_rcu_set(&qemu_logfile, logfile); > } > - qemu_mutex_unlock(&qemu_logfile_mutex); > + logfile = qemu_logfile; Isn't this read outside of the protection of both rcu_read_lock() and the mutex? Could that race? > + > if (qemu_logfile && > (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) { > - qemu_log_close(); > + atomic_rcu_set(&qemu_logfile, NULL); > + call_rcu(logfile, qemu_logfile_free, rcu); I wonder if we can re-arrange the logic here so it's lets confusing? For example the NULL qemu_loglevel can be detected at the start and we should be able just to squash the current log and reset and go. I'm not sure about the damonize/stdout check. > } > + qemu_mutex_unlock(&qemu_logfile_mutex); > } > > void qemu_log_needs_buffers(void) > @@ -123,6 +146,7 @@ void qemu_log_needs_buffers(void) > void qemu_set_log_filename(const char *filename, Error **errp) > { > char *pidstr; > + > g_free(logfilename); nit: stray newline > > pidstr = strstr(filename, "%"); > @@ -235,19 +259,28 @@ out: > /* fflush() the log file */ > void qemu_log_flush(void) > { > - fflush(qemu_logfile); > + QemuLogFile *logfile; > + > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + fflush(logfile->fd); > + } > + rcu_read_unlock(); > } > > /* Close the log file */ > void qemu_log_close(void) > { > + QemuLogFile *logfile; > + > g_assert(qemu_logfile_mutex.initialized); > qemu_mutex_lock(&qemu_logfile_mutex); > - if (qemu_logfile) { > - if (qemu_logfile != stderr) { > - fclose(qemu_logfile); > - } > - qemu_logfile = NULL; > + logfile = qemu_logfile; > + > + if (logfile) { > + atomic_rcu_set(&qemu_logfile, NULL); > + call_rcu(logfile, qemu_logfile_free, rcu); > } > qemu_mutex_unlock(&qemu_logfile_mutex); > } > diff --git a/include/exec/log.h b/include/exec/log.h > index e2cfd436e6..9bd1e4aa20 100644 > --- a/include/exec/log.h > +++ b/include/exec/log.h > @@ -15,8 +15,15 @@ > */ > static inline void log_cpu_state(CPUState *cpu, int flags) > { > + QemuLogFile *logfile; > + > if (qemu_log_enabled()) { > - cpu_dump_state(cpu, qemu_logfile, flags); > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + cpu_dump_state(cpu, logfile->fd, flags); > + } > + rcu_read_unlock(); > } > } > > @@ -40,19 +47,37 @@ static inline void log_cpu_state_mask(int mask, CPUState *cpu, int flags) > static inline void log_target_disas(CPUState *cpu, target_ulong start, > target_ulong len) > { > - target_disas(qemu_logfile, cpu, start, len); > + QemuLogFile *logfile; > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + target_disas(logfile->fd, cpu, start, len); > + } > + rcu_read_unlock(); > } > > static inline void log_disas(void *code, unsigned long size) > { > - disas(qemu_logfile, code, size); > + QemuLogFile *logfile; > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + disas(logfile->fd, code, size); > + } > + rcu_read_unlock(); > } > > #if defined(CONFIG_USER_ONLY) > /* page_dump() output to the log file: */ > static inline void log_page_dump(void) > { > - page_dump(qemu_logfile); > + QemuLogFile *logfile; > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + page_dump(logfile->fd); > + } > + rcu_read_unlock(); > } > #endif > #endif > diff --git a/tcg/tcg.c b/tcg/tcg.c > index 0511266d85..4f616ba38b 100644 > --- a/tcg/tcg.c > +++ b/tcg/tcg.c > @@ -2114,9 +2114,17 @@ static void tcg_dump_ops(TCGContext *s, bool have_prefs) > } > > if (have_prefs || op->life) { > - for (; col < 40; ++col) { > - putc(' ', qemu_logfile); > + > + QemuLogFile *logfile; > + > + rcu_read_lock(); > + logfile = atomic_rcu_read(&qemu_logfile); > + if (logfile) { > + for (; col < 40; ++col) { > + putc(' ', logfile->fd); > + } > } > + rcu_read_unlock(); > } > > if (op->life) { -- Alex Bennée
On Tue, 12 Nov 2019 at 12:36, Alex Bennée <alex.bennee@linaro.org> wrote: > > > > } > > + atomic_rcu_set(&qemu_logfile, logfile); > > } > > - qemu_mutex_unlock(&qemu_logfile_mutex); > > + logfile = qemu_logfile; > > Isn't this read outside of the protection of both rcu_read_lock() and > the mutex? Could that race? This assignment is under the mutex. This change moved the mutex unlock towards the end of the function, just a few lines below the call_rcu(). > > + > > if (qemu_logfile && > > (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) { > > - qemu_log_close(); > > + atomic_rcu_set(&qemu_logfile, NULL); > > + call_rcu(logfile, qemu_logfile_free, rcu); > > I wonder if we can re-arrange the logic here so it's lets confusing? For > example the NULL qemu_loglevel can be detected at the start and we > should be able just to squash the current log and reset and go. I'm not > sure about the damonize/stdout check. > > > } > > + qemu_mutex_unlock(&qemu_logfile_mutex); > > } > > Absolutely, the logic that was here originally can be improved. We found it confusing also. We could move things around a bit and change it to something like this to help clarify. bool need_to_open_file = false; /* * In all cases we only log if qemu_loglevel is set. * And: * If not daemonized we will always log either to stderr * or to a file (if there is a logfilename). * If we are daemonized, * we will only log if there is a logfilename. */ if (qemu_loglevel && (!is_daemonized() || logfilename) { need_to_open_file = true; } g_assert(qemu_logfile_mutex.initialized); qemu_mutex_lock(&qemu_logfile_mutex); if(qemu_logfile && !need_to_open_file) { /* Close file. */ QemuLogFile *logfile = qemu_logfile; atomic_rcu_set(&qemu_logfile, NULL); call_rcu(logfile, qemu_logfile_free, rcu); } else if(!qemu_logfile && need_to_open_file) { logfile = g_new0(QemuLogFile, 1); __snip__ existing patch logic for opening the qemu_logfile will be inserted here. } qemu_mutex_unlock(&qemu_logfile_mutex); > > { > > char *pidstr; > > + > > g_free(logfilename); > > nit: stray newline Will remove the newline. Thanks, Rob On Tue, 12 Nov 2019 at 12:36, Alex Bennée <alex.bennee@linaro.org> wrote: > > > Robert Foley <robert.foley@linaro.org> writes: > > > This now allows changing the logfile while logging is active, > > and also solves the issue of a seg fault while changing the logfile. > > > > Any read access to the qemu_logfile handle will use > > the rcu_read_lock()/unlock() around the use of the handle. > > To fetch the handle we will use atomic_rcu_read(). > > We also in many cases do a check for validity of the > > logfile handle before using it to deal with the case where the > > file is closed and set to NULL. > > > > The cases where we write to the qemu_logfile will use atomic_rcu_set(). > > Writers will also use call_rcu() with a newly added qemu_logfile_free > > function for freeing/closing when readers have finished. > > > > Signed-off-by: Robert Foley <robert.foley@linaro.org> > > --- > > v1 > > - Changes for review comments. > > - Minor changes to definition of QemuLogFile. > > - Changed qemu_log_separate() to fix unbalanced and > > remove qemu_log_enabled() check. > > - changed qemu_log_lock() to include else. > > - make qemu_logfile_free static. > > - use g_assert(logfile) in qemu_logfile_free. > > - Relocated unlock out of if/else in qemu_log_close(), and > > in qemu_set_log(). > > --- > > include/qemu/log.h | 42 ++++++++++++++++++++++---- > > util/log.c | 73 +++++++++++++++++++++++++++++++++------------- > > include/exec/log.h | 33 ++++++++++++++++++--- > > tcg/tcg.c | 12 ++++++-- > > 4 files changed, 128 insertions(+), 32 deletions(-) > > > > diff --git a/include/qemu/log.h b/include/qemu/log.h > > index a7c5b01571..528e1f9dd7 100644 > > --- a/include/qemu/log.h > > +++ b/include/qemu/log.h > > @@ -3,9 +3,16 @@ > > > > /* A small part of this API is split into its own header */ > > #include "qemu/log-for-trace.h" > > +#include "qemu/rcu.h" > > + > > +typedef struct QemuLogFile { > > + struct rcu_head rcu; > > + FILE *fd; > > +} QemuLogFile; > > > > /* Private global variable, don't use */ > > -extern FILE *qemu_logfile; > > +extern QemuLogFile *qemu_logfile; > > + > > > > /* > > * The new API: > > @@ -25,7 +32,16 @@ static inline bool qemu_log_enabled(void) > > */ > > static inline bool qemu_log_separate(void) > > { > > - return qemu_logfile != NULL && qemu_logfile != stderr; > > + QemuLogFile *logfile; > > + bool res = false; > > + > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile && logfile->fd != stderr) { > > + res = true; > > + } > > + rcu_read_unlock(); > > + return res; > > } > > > > #define CPU_LOG_TB_OUT_ASM (1 << 0) > > @@ -55,14 +71,23 @@ static inline bool qemu_log_separate(void) > > > > static inline FILE *qemu_log_lock(void) > > { > > - qemu_flockfile(qemu_logfile); > > - return logfile->fd; > > + QemuLogFile *logfile; > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > + qemu_flockfile(logfile->fd); > > + return logfile->fd; > > + } else { > > + rcu_read_unlock(); > > + return NULL; > > + } > > } > > > > static inline void qemu_log_unlock(FILE *fd) > > { > > if (fd) { > > qemu_funlockfile(fd); > > + rcu_read_unlock(); > > } > > } > > > > @@ -73,9 +98,14 @@ static inline void qemu_log_unlock(FILE *fd) > > static inline void GCC_FMT_ATTR(1, 0) > > qemu_log_vprintf(const char *fmt, va_list va) > > { > > - if (qemu_logfile) { > > - vfprintf(qemu_logfile, fmt, va); > > + QemuLogFile *logfile; > > + > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > + vfprintf(logfile->fd, fmt, va); > > } > > + rcu_read_unlock(); > > } > > > > /* log only if a bit is set on the current loglevel mask: > > diff --git a/util/log.c b/util/log.c > > index c25643dc99..802b8de42e 100644 > > --- a/util/log.c > > +++ b/util/log.c > > @@ -28,7 +28,7 @@ > > > > static char *logfilename; > > static QemuMutex qemu_logfile_mutex; > > -FILE *qemu_logfile; > > +QemuLogFile *qemu_logfile; > > int qemu_loglevel; > > static int log_append = 0; > > static GArray *debug_regions; > > @@ -37,10 +37,14 @@ static GArray *debug_regions; > > int qemu_log(const char *fmt, ...) > > { > > int ret = 0; > > - if (qemu_logfile) { > > + QemuLogFile *logfile; > > + > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > va_list ap; > > va_start(ap, fmt); > > - ret = vfprintf(qemu_logfile, fmt, ap); > > + ret = vfprintf(logfile->fd, fmt, ap); > > va_end(ap); > > > > /* Don't pass back error results. */ > > @@ -48,6 +52,7 @@ int qemu_log(const char *fmt, ...) > > ret = 0; > > } > > } > > + rcu_read_unlock(); > > return ret; > > } > > > > @@ -56,11 +61,23 @@ static void __attribute__((__constructor__)) qemu_logfile_init(void) > > qemu_mutex_init(&qemu_logfile_mutex); > > } > > > > +static void qemu_logfile_free(QemuLogFile *logfile) > > +{ > > + g_assert(logfile); > > + > > + if (logfile->fd != stderr) { > > + fclose(logfile->fd); > > + } > > + g_free(logfile); > > +} > > + > > static bool log_uses_own_buffers; > > > > /* enable or disable low levels log */ > > void qemu_set_log(int log_flags) > > { > > + QemuLogFile *logfile; > > + > > qemu_loglevel = log_flags; > > #ifdef CONFIG_TRACE_LOG > > qemu_loglevel |= LOG_TRACE; > > @@ -70,44 +87,50 @@ void qemu_set_log(int log_flags) > > qemu_mutex_lock(&qemu_logfile_mutex); > > if (!qemu_logfile && > > (is_daemonized() ? logfilename != NULL : qemu_loglevel)) { > > + logfile = g_new0(QemuLogFile, 1); > > if (logfilename) { > > - qemu_logfile = fopen(logfilename, log_append ? "a" : "w"); > > - if (!qemu_logfile) { > > + logfile->fd = fopen(logfilename, log_append ? "a" : "w"); > > + if (!logfile->fd) { > > + g_free(logfile); > > perror(logfilename); > > _exit(1); > > } > > /* In case we are a daemon redirect stderr to logfile */ > > if (is_daemonized()) { > > - dup2(fileno(qemu_logfile), STDERR_FILENO); > > - fclose(qemu_logfile); > > + dup2(fileno(logfile->fd), STDERR_FILENO); > > + fclose(logfile->fd); > > /* This will skip closing logfile in qemu_log_close() */ > > - qemu_logfile = stderr; > > + logfile->fd = stderr; > > } > > } else { > > /* Default to stderr if no log file specified */ > > assert(!is_daemonized()); > > - qemu_logfile = stderr; > > + logfile->fd = stderr; > > } > > /* must avoid mmap() usage of glibc by setting a buffer "by hand" */ > > if (log_uses_own_buffers) { > > static char logfile_buf[4096]; > > > > - setvbuf(qemu_logfile, logfile_buf, _IOLBF, sizeof(logfile_buf)); > > + setvbuf(logfile->fd, logfile_buf, _IOLBF, sizeof(logfile_buf)); > > } else { > > #if defined(_WIN32) > > /* Win32 doesn't support line-buffering, so use unbuffered output. */ > > - setvbuf(qemu_logfile, NULL, _IONBF, 0); > > + setvbuf(logfile->fd, NULL, _IONBF, 0); > > #else > > - setvbuf(qemu_logfile, NULL, _IOLBF, 0); > > + setvbuf(logfile->fd, NULL, _IOLBF, 0); > > #endif > > log_append = 1; > > } > > + atomic_rcu_set(&qemu_logfile, logfile); > > } > > - qemu_mutex_unlock(&qemu_logfile_mutex); > > + logfile = qemu_logfile; > > Isn't this read outside of the protection of both rcu_read_lock() and > the mutex? Could that race? > > > + > > if (qemu_logfile && > > (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) { > > - qemu_log_close(); > > + atomic_rcu_set(&qemu_logfile, NULL); > > + call_rcu(logfile, qemu_logfile_free, rcu); > > I wonder if we can re-arrange the logic here so it's lets confusing? For > example the NULL qemu_loglevel can be detected at the start and we > should be able just to squash the current log and reset and go. I'm not > sure about the damonize/stdout check. > > > } > > + qemu_mutex_unlock(&qemu_logfile_mutex); > > } > > > > void qemu_log_needs_buffers(void) > > @@ -123,6 +146,7 @@ void qemu_log_needs_buffers(void) > > void qemu_set_log_filename(const char *filename, Error **errp) > > { > > char *pidstr; > > + > > g_free(logfilename); > > nit: stray newline > > > > pidstr = strstr(filename, "%"); > > @@ -235,19 +259,28 @@ out: > > /* fflush() the log file */ > > void qemu_log_flush(void) > > { > > - fflush(qemu_logfile); > > + QemuLogFile *logfile; > > + > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > + fflush(logfile->fd); > > + } > > + rcu_read_unlock(); > > } > > > > /* Close the log file */ > > void qemu_log_close(void) > > { > > + QemuLogFile *logfile; > > + > > g_assert(qemu_logfile_mutex.initialized); > > qemu_mutex_lock(&qemu_logfile_mutex); > > - if (qemu_logfile) { > > - if (qemu_logfile != stderr) { > > - fclose(qemu_logfile); > > - } > > - qemu_logfile = NULL; > > + logfile = qemu_logfile; > > + > > + if (logfile) { > > + atomic_rcu_set(&qemu_logfile, NULL); > > + call_rcu(logfile, qemu_logfile_free, rcu); > > } > > qemu_mutex_unlock(&qemu_logfile_mutex); > > } > > diff --git a/include/exec/log.h b/include/exec/log.h > > index e2cfd436e6..9bd1e4aa20 100644 > > --- a/include/exec/log.h > > +++ b/include/exec/log.h > > @@ -15,8 +15,15 @@ > > */ > > static inline void log_cpu_state(CPUState *cpu, int flags) > > { > > + QemuLogFile *logfile; > > + > > if (qemu_log_enabled()) { > > - cpu_dump_state(cpu, qemu_logfile, flags); > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > + cpu_dump_state(cpu, logfile->fd, flags); > > + } > > + rcu_read_unlock(); > > } > > } > > > > @@ -40,19 +47,37 @@ static inline void log_cpu_state_mask(int mask, CPUState *cpu, int flags) > > static inline void log_target_disas(CPUState *cpu, target_ulong start, > > target_ulong len) > > { > > - target_disas(qemu_logfile, cpu, start, len); > > + QemuLogFile *logfile; > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > + target_disas(logfile->fd, cpu, start, len); > > + } > > + rcu_read_unlock(); > > } > > > > static inline void log_disas(void *code, unsigned long size) > > { > > - disas(qemu_logfile, code, size); > > + QemuLogFile *logfile; > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > + disas(logfile->fd, code, size); > > + } > > + rcu_read_unlock(); > > } > > > > #if defined(CONFIG_USER_ONLY) > > /* page_dump() output to the log file: */ > > static inline void log_page_dump(void) > > { > > - page_dump(qemu_logfile); > > + QemuLogFile *logfile; > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > + page_dump(logfile->fd); > > + } > > + rcu_read_unlock(); > > } > > #endif > > #endif > > diff --git a/tcg/tcg.c b/tcg/tcg.c > > index 0511266d85..4f616ba38b 100644 > > --- a/tcg/tcg.c > > +++ b/tcg/tcg.c > > @@ -2114,9 +2114,17 @@ static void tcg_dump_ops(TCGContext *s, bool have_prefs) > > } > > > > if (have_prefs || op->life) { > > - for (; col < 40; ++col) { > > - putc(' ', qemu_logfile); > > + > > + QemuLogFile *logfile; > > + > > + rcu_read_lock(); > > + logfile = atomic_rcu_read(&qemu_logfile); > > + if (logfile) { > > + for (; col < 40; ++col) { > > + putc(' ', logfile->fd); > > + } > > } > > + rcu_read_unlock(); > > } > > > > if (op->life) { > > > -- > Alex Bennée
Robert Foley <robert.foley@linaro.org> writes: > On Tue, 12 Nov 2019 at 12:36, Alex Bennée <alex.bennee@linaro.org> wrote: >> >> >> > } >> > + atomic_rcu_set(&qemu_logfile, logfile); >> > } >> > - qemu_mutex_unlock(&qemu_logfile_mutex); >> > + logfile = qemu_logfile; >> >> Isn't this read outside of the protection of both rcu_read_lock() and >> the mutex? Could that race? > > This assignment is under the mutex. This change moved the mutex > unlock towards the end of the function, just a few lines below the > call_rcu(). Ahh I see now, I went +- blind ;-) > >> > + >> > if (qemu_logfile && >> > (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) { >> > - qemu_log_close(); >> > + atomic_rcu_set(&qemu_logfile, NULL); >> > + call_rcu(logfile, qemu_logfile_free, rcu); >> >> I wonder if we can re-arrange the logic here so it's lets confusing? For >> example the NULL qemu_loglevel can be detected at the start and we >> should be able just to squash the current log and reset and go. I'm not >> sure about the damonize/stdout check. >> >> > } >> > + qemu_mutex_unlock(&qemu_logfile_mutex); >> > } >> > > > Absolutely, the logic that was here originally can be improved. We > found it confusing also. > We could move things around a bit and change it to something like this > to help clarify. > > bool need_to_open_file = false; > /* > * In all cases we only log if qemu_loglevel is set. > * And: > * If not daemonized we will always log either to stderr > * or to a file (if there is a logfilename). > * If we are daemonized, > * we will only log if there is a logfilename. > */ > if (qemu_loglevel && (!is_daemonized() || logfilename) { > need_to_open_file = true; > } > g_assert(qemu_logfile_mutex.initialized); > qemu_mutex_lock(&qemu_logfile_mutex); > > if(qemu_logfile && !need_to_open_file) { > /* Close file. */ > QemuLogFile *logfile = qemu_logfile; > atomic_rcu_set(&qemu_logfile, NULL); > call_rcu(logfile, qemu_logfile_free, rcu); > } else if(!qemu_logfile && need_to_open_file) { > logfile = g_new0(QemuLogFile, 1); > __snip__ existing patch logic for opening the qemu_logfile will > be inserted here. > } > qemu_mutex_unlock(&qemu_logfile_mutex); That reads a lot better thanks. It's probably worth doing the clean-up in a separate patch so it is easier to see the mutex's when added. -- Alex Bennée
diff --git a/include/qemu/log.h b/include/qemu/log.h index a7c5b01571..528e1f9dd7 100644 --- a/include/qemu/log.h +++ b/include/qemu/log.h @@ -3,9 +3,16 @@ /* A small part of this API is split into its own header */ #include "qemu/log-for-trace.h" +#include "qemu/rcu.h" + +typedef struct QemuLogFile { + struct rcu_head rcu; + FILE *fd; +} QemuLogFile; /* Private global variable, don't use */ -extern FILE *qemu_logfile; +extern QemuLogFile *qemu_logfile; + /* * The new API: @@ -25,7 +32,16 @@ static inline bool qemu_log_enabled(void) */ static inline bool qemu_log_separate(void) { - return qemu_logfile != NULL && qemu_logfile != stderr; + QemuLogFile *logfile; + bool res = false; + + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile && logfile->fd != stderr) { + res = true; + } + rcu_read_unlock(); + return res; } #define CPU_LOG_TB_OUT_ASM (1 << 0) @@ -55,14 +71,23 @@ static inline bool qemu_log_separate(void) static inline FILE *qemu_log_lock(void) { - qemu_flockfile(qemu_logfile); - return logfile->fd; + QemuLogFile *logfile; + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { + qemu_flockfile(logfile->fd); + return logfile->fd; + } else { + rcu_read_unlock(); + return NULL; + } } static inline void qemu_log_unlock(FILE *fd) { if (fd) { qemu_funlockfile(fd); + rcu_read_unlock(); } } @@ -73,9 +98,14 @@ static inline void qemu_log_unlock(FILE *fd) static inline void GCC_FMT_ATTR(1, 0) qemu_log_vprintf(const char *fmt, va_list va) { - if (qemu_logfile) { - vfprintf(qemu_logfile, fmt, va); + QemuLogFile *logfile; + + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { + vfprintf(logfile->fd, fmt, va); } + rcu_read_unlock(); } /* log only if a bit is set on the current loglevel mask: diff --git a/util/log.c b/util/log.c index c25643dc99..802b8de42e 100644 --- a/util/log.c +++ b/util/log.c @@ -28,7 +28,7 @@ static char *logfilename; static QemuMutex qemu_logfile_mutex; -FILE *qemu_logfile; +QemuLogFile *qemu_logfile; int qemu_loglevel; static int log_append = 0; static GArray *debug_regions; @@ -37,10 +37,14 @@ static GArray *debug_regions; int qemu_log(const char *fmt, ...) { int ret = 0; - if (qemu_logfile) { + QemuLogFile *logfile; + + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { va_list ap; va_start(ap, fmt); - ret = vfprintf(qemu_logfile, fmt, ap); + ret = vfprintf(logfile->fd, fmt, ap); va_end(ap); /* Don't pass back error results. */ @@ -48,6 +52,7 @@ int qemu_log(const char *fmt, ...) ret = 0; } } + rcu_read_unlock(); return ret; } @@ -56,11 +61,23 @@ static void __attribute__((__constructor__)) qemu_logfile_init(void) qemu_mutex_init(&qemu_logfile_mutex); } +static void qemu_logfile_free(QemuLogFile *logfile) +{ + g_assert(logfile); + + if (logfile->fd != stderr) { + fclose(logfile->fd); + } + g_free(logfile); +} + static bool log_uses_own_buffers; /* enable or disable low levels log */ void qemu_set_log(int log_flags) { + QemuLogFile *logfile; + qemu_loglevel = log_flags; #ifdef CONFIG_TRACE_LOG qemu_loglevel |= LOG_TRACE; @@ -70,44 +87,50 @@ void qemu_set_log(int log_flags) qemu_mutex_lock(&qemu_logfile_mutex); if (!qemu_logfile && (is_daemonized() ? logfilename != NULL : qemu_loglevel)) { + logfile = g_new0(QemuLogFile, 1); if (logfilename) { - qemu_logfile = fopen(logfilename, log_append ? "a" : "w"); - if (!qemu_logfile) { + logfile->fd = fopen(logfilename, log_append ? "a" : "w"); + if (!logfile->fd) { + g_free(logfile); perror(logfilename); _exit(1); } /* In case we are a daemon redirect stderr to logfile */ if (is_daemonized()) { - dup2(fileno(qemu_logfile), STDERR_FILENO); - fclose(qemu_logfile); + dup2(fileno(logfile->fd), STDERR_FILENO); + fclose(logfile->fd); /* This will skip closing logfile in qemu_log_close() */ - qemu_logfile = stderr; + logfile->fd = stderr; } } else { /* Default to stderr if no log file specified */ assert(!is_daemonized()); - qemu_logfile = stderr; + logfile->fd = stderr; } /* must avoid mmap() usage of glibc by setting a buffer "by hand" */ if (log_uses_own_buffers) { static char logfile_buf[4096]; - setvbuf(qemu_logfile, logfile_buf, _IOLBF, sizeof(logfile_buf)); + setvbuf(logfile->fd, logfile_buf, _IOLBF, sizeof(logfile_buf)); } else { #if defined(_WIN32) /* Win32 doesn't support line-buffering, so use unbuffered output. */ - setvbuf(qemu_logfile, NULL, _IONBF, 0); + setvbuf(logfile->fd, NULL, _IONBF, 0); #else - setvbuf(qemu_logfile, NULL, _IOLBF, 0); + setvbuf(logfile->fd, NULL, _IOLBF, 0); #endif log_append = 1; } + atomic_rcu_set(&qemu_logfile, logfile); } - qemu_mutex_unlock(&qemu_logfile_mutex); + logfile = qemu_logfile; + if (qemu_logfile && (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) { - qemu_log_close(); + atomic_rcu_set(&qemu_logfile, NULL); + call_rcu(logfile, qemu_logfile_free, rcu); } + qemu_mutex_unlock(&qemu_logfile_mutex); } void qemu_log_needs_buffers(void) @@ -123,6 +146,7 @@ void qemu_log_needs_buffers(void) void qemu_set_log_filename(const char *filename, Error **errp) { char *pidstr; + g_free(logfilename); pidstr = strstr(filename, "%"); @@ -235,19 +259,28 @@ out: /* fflush() the log file */ void qemu_log_flush(void) { - fflush(qemu_logfile); + QemuLogFile *logfile; + + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { + fflush(logfile->fd); + } + rcu_read_unlock(); } /* Close the log file */ void qemu_log_close(void) { + QemuLogFile *logfile; + g_assert(qemu_logfile_mutex.initialized); qemu_mutex_lock(&qemu_logfile_mutex); - if (qemu_logfile) { - if (qemu_logfile != stderr) { - fclose(qemu_logfile); - } - qemu_logfile = NULL; + logfile = qemu_logfile; + + if (logfile) { + atomic_rcu_set(&qemu_logfile, NULL); + call_rcu(logfile, qemu_logfile_free, rcu); } qemu_mutex_unlock(&qemu_logfile_mutex); } diff --git a/include/exec/log.h b/include/exec/log.h index e2cfd436e6..9bd1e4aa20 100644 --- a/include/exec/log.h +++ b/include/exec/log.h @@ -15,8 +15,15 @@ */ static inline void log_cpu_state(CPUState *cpu, int flags) { + QemuLogFile *logfile; + if (qemu_log_enabled()) { - cpu_dump_state(cpu, qemu_logfile, flags); + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { + cpu_dump_state(cpu, logfile->fd, flags); + } + rcu_read_unlock(); } } @@ -40,19 +47,37 @@ static inline void log_cpu_state_mask(int mask, CPUState *cpu, int flags) static inline void log_target_disas(CPUState *cpu, target_ulong start, target_ulong len) { - target_disas(qemu_logfile, cpu, start, len); + QemuLogFile *logfile; + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { + target_disas(logfile->fd, cpu, start, len); + } + rcu_read_unlock(); } static inline void log_disas(void *code, unsigned long size) { - disas(qemu_logfile, code, size); + QemuLogFile *logfile; + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { + disas(logfile->fd, code, size); + } + rcu_read_unlock(); } #if defined(CONFIG_USER_ONLY) /* page_dump() output to the log file: */ static inline void log_page_dump(void) { - page_dump(qemu_logfile); + QemuLogFile *logfile; + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { + page_dump(logfile->fd); + } + rcu_read_unlock(); } #endif #endif diff --git a/tcg/tcg.c b/tcg/tcg.c index 0511266d85..4f616ba38b 100644 --- a/tcg/tcg.c +++ b/tcg/tcg.c @@ -2114,9 +2114,17 @@ static void tcg_dump_ops(TCGContext *s, bool have_prefs) } if (have_prefs || op->life) { - for (; col < 40; ++col) { - putc(' ', qemu_logfile); + + QemuLogFile *logfile; + + rcu_read_lock(); + logfile = atomic_rcu_read(&qemu_logfile); + if (logfile) { + for (; col < 40; ++col) { + putc(' ', logfile->fd); + } } + rcu_read_unlock(); } if (op->life) {
This now allows changing the logfile while logging is active, and also solves the issue of a seg fault while changing the logfile. Any read access to the qemu_logfile handle will use the rcu_read_lock()/unlock() around the use of the handle. To fetch the handle we will use atomic_rcu_read(). We also in many cases do a check for validity of the logfile handle before using it to deal with the case where the file is closed and set to NULL. The cases where we write to the qemu_logfile will use atomic_rcu_set(). Writers will also use call_rcu() with a newly added qemu_logfile_free function for freeing/closing when readers have finished. Signed-off-by: Robert Foley <robert.foley@linaro.org> --- v1 - Changes for review comments. - Minor changes to definition of QemuLogFile. - Changed qemu_log_separate() to fix unbalanced and remove qemu_log_enabled() check. - changed qemu_log_lock() to include else. - make qemu_logfile_free static. - use g_assert(logfile) in qemu_logfile_free. - Relocated unlock out of if/else in qemu_log_close(), and in qemu_set_log(). --- include/qemu/log.h | 42 ++++++++++++++++++++++---- util/log.c | 73 +++++++++++++++++++++++++++++++++------------- include/exec/log.h | 33 ++++++++++++++++++--- tcg/tcg.c | 12 ++++++-- 4 files changed, 128 insertions(+), 32 deletions(-)