| Message ID | 20220427224924.592546-19-gpiccoli@igalia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | The panic notifiers refactor | expand |
On 2022/4/28 6:49, Guilherme G. Piccoli wrote: > Currently we have a debug infrastructure in the notifiers file, but > it's very simple/limited. This patch extends it by: > > (a) Showing all registered/unregistered notifiers' callback names; > > (b) Adding a dynamic debug tuning to allow showing called notifiers' > function names. Notice that this should be guarded as a tunable since > it can flood the kernel log buffer. > > Cc: Arjan van de Ven <arjan@linux.intel.com> > Cc: Cong Wang <xiyou.wangcong@gmail.com> > Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Cc: Valentin Schneider <valentin.schneider@arm.com> > Cc: Xiaoming Ni <nixiaoming@huawei.com> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> > --- > > We have some design decisions that worth discussing here: > > (a) First of call, using C99 helps a lot to write clear and concise code, but > due to commit 4d94f910e79a ("Kbuild: use -Wdeclaration-after-statement") we > have a warning if mixing variable declarations with code. For this patch though, > doing that makes the code way clear, so decision was to add the debug code > inside brackets whenever this warning pops up. We can change that, but that'll > cause more ifdefs in the same function. > > (b) In the symbol lookup helper function, we modify the parameter passed but > even more, we return it as well! This is unusual and seems unnecessary, but was > the strategy taken to allow embedding such function in the pr_debug() call. > > Not doing that would likely requiring 3 symbol_name variables to avoid > concurrency (registering notifier A while calling notifier B) - we rely in > local variables as a serialization mechanism. > > We're open for suggestions in case this design is not appropriate; > thanks in advance! > > kernel/notifier.c | 48 +++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 46 insertions(+), 2 deletions(-) > > diff --git a/kernel/notifier.c b/kernel/notifier.c > index ba005ebf4730..21032ebcde57 100644 > --- a/kernel/notifier.c > +++ b/kernel/notifier.c > @@ -7,6 +7,22 @@ > #include <linux/vmalloc.h> > #include <linux/reboot.h> > > +#ifdef CONFIG_DEBUG_NOTIFIERS > +#include <linux/kallsyms.h> > + > +/* > + * Helper to get symbol names in case DEBUG_NOTIFIERS is set. > + * Return the modified parameter is a strategy used to achieve > + * the pr_debug() functionality - with this, function is only > + * executed if the dynamic debug tuning is effectively set. > + */ > +static inline char *notifier_name(struct notifier_block *nb, char *sym_name) > +{ > + lookup_symbol_name((unsigned long)(nb->notifier_call), sym_name); > + return sym_name; > +} > +#endif > + > /* > * Notifier list for kernel code which wants to be called > * at shutdown. This is used to stop any idling DMA operations > @@ -34,20 +50,41 @@ static int notifier_chain_register(struct notifier_block **nl, > } > n->next = *nl; > rcu_assign_pointer(*nl, n); > + > +#ifdef CONFIG_DEBUG_NOTIFIERS > + { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_info("notifiers: registered %s()\n", > + notifier_name(n, sym_name)); > + } Duplicate Code. Is it better to use __func__ and %pS? pr_info("%s: %pS\n", __func__, n->notifier_call); > +#endif > return 0; > } > > static int notifier_chain_unregister(struct notifier_block **nl, > struct notifier_block *n) > { > + int ret = -ENOENT; > + > while ((*nl) != NULL) { > if ((*nl) == n) { > rcu_assign_pointer(*nl, n->next); > - return 0; > + ret = 0; > + break; > } > nl = &((*nl)->next); > } > - return -ENOENT; > + > +#ifdef CONFIG_DEBUG_NOTIFIERS > + if (!ret) { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_info("notifiers: unregistered %s()\n", > + notifier_name(n, sym_name)); > + } Duplicate Code. Is it better to use __func__ and %pS? pr_info("%s: %pS\n", __func__, n->notifier_call); > +#endif > + return ret; > } > > /** > @@ -80,6 +117,13 @@ static int notifier_call_chain(struct notifier_block **nl, > nb = next_nb; > continue; > } > + Is the "#ifdef" missing here? > + { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_debug("notifiers: calling %s()\n", > + notifier_name(nb, sym_name)); Duplicate Code. Is it better to use __func__ and %pS? pr_info("%s: %pS\n", __func__, n->notifier_call); > + } > #endif > ret = nb->notifier_call(nb, val, v); > > Thanks Xiaoming Ni
From: Guilherme G. Piccoli <gpiccoli@igalia.com> Sent: Wednesday, April 27, 2022 3:49 PM > > Currently we have a debug infrastructure in the notifiers file, but > it's very simple/limited. This patch extends it by: > > (a) Showing all registered/unregistered notifiers' callback names; > > (b) Adding a dynamic debug tuning to allow showing called notifiers' > function names. Notice that this should be guarded as a tunable since > it can flood the kernel log buffer. > > Cc: Arjan van de Ven <arjan@linux.intel.com> > Cc: Cong Wang <xiyou.wangcong@gmail.com> > Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Cc: Valentin Schneider <valentin.schneider@arm.com> > Cc: Xiaoming Ni <nixiaoming@huawei.com> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> > --- > > We have some design decisions that worth discussing here: > > (a) First of call, using C99 helps a lot to write clear and concise code, but s/call/all/ > due to commit 4d94f910e79a ("Kbuild: use -Wdeclaration-after-statement") we > have a warning if mixing variable declarations with code. For this patch though, > doing that makes the code way clear, so decision was to add the debug code > inside brackets whenever this warning pops up. We can change that, but that'll > cause more ifdefs in the same function. > > (b) In the symbol lookup helper function, we modify the parameter passed but > even more, we return it as well! This is unusual and seems unnecessary, but was > the strategy taken to allow embedding such function in the pr_debug() call. > > Not doing that would likely requiring 3 symbol_name variables to avoid > concurrency (registering notifier A while calling notifier B) - we rely in > local variables as a serialization mechanism. > > We're open for suggestions in case this design is not appropriate; > thanks in advance! > > kernel/notifier.c | 48 +++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 46 insertions(+), 2 deletions(-) > > diff --git a/kernel/notifier.c b/kernel/notifier.c > index ba005ebf4730..21032ebcde57 100644 > --- a/kernel/notifier.c > +++ b/kernel/notifier.c > @@ -7,6 +7,22 @@ > #include <linux/vmalloc.h> > #include <linux/reboot.h> > > +#ifdef CONFIG_DEBUG_NOTIFIERS > +#include <linux/kallsyms.h> > + > +/* > + * Helper to get symbol names in case DEBUG_NOTIFIERS is set. > + * Return the modified parameter is a strategy used to achieve > + * the pr_debug() functionality - with this, function is only > + * executed if the dynamic debug tuning is effectively set. > + */ > +static inline char *notifier_name(struct notifier_block *nb, char *sym_name) > +{ > + lookup_symbol_name((unsigned long)(nb->notifier_call), sym_name); > + return sym_name; > +} > +#endif > + > /* > * Notifier list for kernel code which wants to be called > * at shutdown. This is used to stop any idling DMA operations > @@ -34,20 +50,41 @@ static int notifier_chain_register(struct notifier_block **nl, > } > n->next = *nl; > rcu_assign_pointer(*nl, n); > + > +#ifdef CONFIG_DEBUG_NOTIFIERS > + { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_info("notifiers: registered %s()\n", > + notifier_name(n, sym_name)); > + } > +#endif > return 0; > } > > static int notifier_chain_unregister(struct notifier_block **nl, > struct notifier_block *n) > { > + int ret = -ENOENT; > + > while ((*nl) != NULL) { > if ((*nl) == n) { > rcu_assign_pointer(*nl, n->next); > - return 0; > + ret = 0; > + break; > } > nl = &((*nl)->next); > } > - return -ENOENT; > + > +#ifdef CONFIG_DEBUG_NOTIFIERS > + if (!ret) { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_info("notifiers: unregistered %s()\n", > + notifier_name(n, sym_name)); > + } > +#endif > + return ret; > } > > /** > @@ -80,6 +117,13 @@ static int notifier_call_chain(struct notifier_block **nl, > nb = next_nb; > continue; > } > + > + { > + char sym_name[KSYM_NAME_LEN]; > + > + pr_debug("notifiers: calling %s()\n", > + notifier_name(nb, sym_name)); > + } > #endif > ret = nb->notifier_call(nb, val, v); > > -- > 2.36.0
On 27/04/2022 22:01, Xiaoming Ni wrote: > [...] > Duplicate Code. > > Is it better to use __func__ and %pS? > > pr_info("%s: %pS\n", __func__, n->notifier_call); > > This is a great suggestion Xiaoming, much appreciated! I feel like reinventing the wheel here - with your idea, code was super clear and concise, very nice suggestion!! The only 2 things that diverge from your idea: I'm using '%ps' (not showing offsets) and also, kept the wording "(un)registered/calling", not using __func__ - I feel it's a bit odd in the output. OK for you? I'm definitely using your idea in V2 heh Cheers, Guilherme
On Thu, 28 Apr 2022 09:01:13 +0800 Xiaoming Ni <nixiaoming@huawei.com> wrote: > > +#ifdef CONFIG_DEBUG_NOTIFIERS > > + { > > + char sym_name[KSYM_NAME_LEN]; > > + > > + pr_info("notifiers: registered %s()\n", > > + notifier_name(n, sym_name)); > > + } > > Duplicate Code. > > Is it better to use __func__ and %pS? > > pr_info("%s: %pS\n", __func__, n->notifier_call); > > > > +#endif Also, don't sprinkle #ifdef in C code. Instead: if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS)) pr_info("notifers: regsiter %ps()\n", n->notifer_call); Or define a print macro at the start of the C file that is a nop if it is not defined, and use the macro. -- Steve
On 10/05/2022 14:29, Steven Rostedt wrote: > [...] > Also, don't sprinkle #ifdef in C code. Instead: > > if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS)) > pr_info("notifers: regsiter %ps()\n", > n->notifer_call); > > > Or define a print macro at the start of the C file that is a nop if it is > not defined, and use the macro. Thanks, I'll go with the IS_ENABLED() idea in V2 - appreciate the hint. Cheers, Guilherme
diff --git a/kernel/notifier.c b/kernel/notifier.c index ba005ebf4730..21032ebcde57 100644 --- a/kernel/notifier.c +++ b/kernel/notifier.c @@ -7,6 +7,22 @@ #include <linux/vmalloc.h> #include <linux/reboot.h> +#ifdef CONFIG_DEBUG_NOTIFIERS +#include <linux/kallsyms.h> + +/* + * Helper to get symbol names in case DEBUG_NOTIFIERS is set. + * Return the modified parameter is a strategy used to achieve + * the pr_debug() functionality - with this, function is only + * executed if the dynamic debug tuning is effectively set. + */ +static inline char *notifier_name(struct notifier_block *nb, char *sym_name) +{ + lookup_symbol_name((unsigned long)(nb->notifier_call), sym_name); + return sym_name; +} +#endif + /* * Notifier list for kernel code which wants to be called * at shutdown. This is used to stop any idling DMA operations @@ -34,20 +50,41 @@ static int notifier_chain_register(struct notifier_block **nl, } n->next = *nl; rcu_assign_pointer(*nl, n); + +#ifdef CONFIG_DEBUG_NOTIFIERS + { + char sym_name[KSYM_NAME_LEN]; + + pr_info("notifiers: registered %s()\n", + notifier_name(n, sym_name)); + } +#endif return 0; } static int notifier_chain_unregister(struct notifier_block **nl, struct notifier_block *n) { + int ret = -ENOENT; + while ((*nl) != NULL) { if ((*nl) == n) { rcu_assign_pointer(*nl, n->next); - return 0; + ret = 0; + break; } nl = &((*nl)->next); } - return -ENOENT; + +#ifdef CONFIG_DEBUG_NOTIFIERS + if (!ret) { + char sym_name[KSYM_NAME_LEN]; + + pr_info("notifiers: unregistered %s()\n", + notifier_name(n, sym_name)); + } +#endif + return ret; } /** @@ -80,6 +117,13 @@ static int notifier_call_chain(struct notifier_block **nl, nb = next_nb; continue; } + + { + char sym_name[KSYM_NAME_LEN]; + + pr_debug("notifiers: calling %s()\n", + notifier_name(nb, sym_name)); + } #endif ret = nb->notifier_call(nb, val, v);
Currently we have a debug infrastructure in the notifiers file, but it's very simple/limited. This patch extends it by: (a) Showing all registered/unregistered notifiers' callback names; (b) Adding a dynamic debug tuning to allow showing called notifiers' function names. Notice that this should be guarded as a tunable since it can flood the kernel log buffer. Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Cong Wang <xiyou.wangcong@gmail.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Valentin Schneider <valentin.schneider@arm.com> Cc: Xiaoming Ni <nixiaoming@huawei.com> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> --- We have some design decisions that worth discussing here: (a) First of call, using C99 helps a lot to write clear and concise code, but due to commit 4d94f910e79a ("Kbuild: use -Wdeclaration-after-statement") we have a warning if mixing variable declarations with code. For this patch though, doing that makes the code way clear, so decision was to add the debug code inside brackets whenever this warning pops up. We can change that, but that'll cause more ifdefs in the same function. (b) In the symbol lookup helper function, we modify the parameter passed but even more, we return it as well! This is unusual and seems unnecessary, but was the strategy taken to allow embedding such function in the pr_debug() call. Not doing that would likely requiring 3 symbol_name variables to avoid concurrency (registering notifier A while calling notifier B) - we rely in local variables as a serialization mechanism. We're open for suggestions in case this design is not appropriate; thanks in advance! kernel/notifier.c | 48 +++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 46 insertions(+), 2 deletions(-)