| Message ID | 1502082623-23952-1-git-send-email-hoeun.ryu@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Hoeun, On 07/08/17 06:09, Hoeun Ryu wrote: > Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly > version in panic path) introduced crash_smp_send_stop() which is a weak > function and can be overriden by architecture codes to fix the side effect (overridden) > caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_ > notifiers" option). > > ARM64 architecture uses the weak version function and the problem is that > the weak function simply calls smp_send_stop() which makes other CPUs > offline and takes away the chance to save crash information for nonpanic > CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel > option is enabled. > > Calling smp_send_crash_stop() in machine_crash_shutdown() is useless > because all nonpanic CPUs are already offline by smp_send_stop() in this > case and smp_send_crash_stop() only works against online CPUs. > The result is that /proc/vmcore is not available with the error messages; > "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized". When I tried this I got one of these warnings for each secondary CPU, but the vmcore file was still available. When I ran 'crash' on the vmcore it reported: > CPUS: 6 [OFFLINE: 5] Did I miss as step to reproduce this? If not, can we change this paragraph to say something like: > The result is that secondary CPUs registers are not saved by crash_save_cpu() > and the vmcore file misreports these CPUs as being offline. > crash_smp_send_stop() is implemented to fix this problem by replacing the > exising smp_send_crash_stop() and adding a check for multiple calling to (existing) > the function. The function (strong symbol version) saves crash information > for nonpanic CPUs and machine_crash_shutdown() tries to save crash > information for nonpanic CPUs only when crash_kexec_post_notifiers kernel > option is disabled. > > * crash_kexec_post_notifiers : false > > panic() > __crash_kexec() > machine_crash_shutdown() > crash_smp_send_stop() <= save crash dump for nonpanic cores > > * crash_kexec_post_notifiers : true > > panic() > crash_smp_send_stop() <= save crash dump for nonpanic cores > __crash_kexec() > machine_crash_shutdown() > crash_smp_send_stop() <= just return. > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > index dc66e6e..73d8f5e 100644 > --- a/arch/arm64/kernel/smp.c > +++ b/arch/arm64/kernel/smp.c > @@ -977,11 +977,21 @@ void smp_send_stop(void) > } > > #ifdef CONFIG_KEXEC_CORE > -void smp_send_crash_stop(void) > +void crash_smp_send_stop(void) > { > + static int cpus_stopped; > cpumask_t mask; > unsigned long timeout; > > + /* > + * This function can be called twice in panic path, but obviously > + * we execute this only once. > + */ > + if (cpus_stopped) > + return; > + > + cpus_stopped = 1; > + This cpus_stopped=1 can't happen on multiple CPUs at the same time as any second call is guaranteed to be on the same CPU, both are behind panic()s 'atomic_cmpxchg()'. Other than my '/proc/vmcore is not available' question above, this looks fine to me: Reviewed-by: James Morse <james.morse@arm.com> Tested-by: James Morse <james.morse@arm.com> Thanks! James
Hello, James. Thank you for the meticulous test and review. On Fri, 2017-08-11 at 18:02 +0100, James Morse wrote: > Hi Hoeun, > > On 07/08/17 06:09, Hoeun Ryu wrote: > > > > Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly > > version in panic path) introduced crash_smp_send_stop() which is a weak > > function and can be overriden by architecture codes to fix the side effect > (overridden) It'll be fixed in the next version. > > > > > > caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_ > > notifiers" option). > > > > ARM64 architecture uses the weak version function and the problem is that > > the weak function simply calls smp_send_stop() which makes other CPUs > > offline and takes away the chance to save crash information for nonpanic > > CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel > > option is enabled. > > > > Calling smp_send_crash_stop() in machine_crash_shutdown() is useless > > because all nonpanic CPUs are already offline by smp_send_stop() in this > > case and smp_send_crash_stop() only works against online CPUs. > > > > > The result is that /proc/vmcore is not available with the error messages; > > "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized". > When I tried this I got one of these warnings for each secondary CPU, but the > vmcore file was still available. When I ran 'crash' on the vmcore it reported: > > > > CPUS: 6 [OFFLINE: 5] > Did I miss as step to reproduce this? If not, can we change this paragraph to > say something like: > > > > The result is that secondary CPUs registers are not saved by crash_save_cpu() > > and the vmcore file misreports these CPUs as being offline. Actually the commit log comes from the patch to fix a similar issue in arm port. I'll change the commit log with yours. > > > > > crash_smp_send_stop() is implemented to fix this problem by replacing the > > exising smp_send_crash_stop() and adding a check for multiple calling to > (existing) It'll be fixed in the next version. > > > > > > the function. The function (strong symbol version) saves crash information > > for nonpanic CPUs and machine_crash_shutdown() tries to save crash > > information for nonpanic CPUs only when crash_kexec_post_notifiers kernel > > option is disabled. > > > > * crash_kexec_post_notifiers : false > > > > panic() > > __crash_kexec() > > machine_crash_shutdown() > > crash_smp_send_stop() <= save crash dump for nonpanic cores > > > > * crash_kexec_post_notifiers : true > > > > panic() > > crash_smp_send_stop() <= save crash dump for nonpanic cores > > __crash_kexec() > > machine_crash_shutdown() > > crash_smp_send_stop() <= just return. > > > > > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > > index dc66e6e..73d8f5e 100644 > > --- a/arch/arm64/kernel/smp.c > > +++ b/arch/arm64/kernel/smp.c > > @@ -977,11 +977,21 @@ void smp_send_stop(void) > > } > > > > #ifdef CONFIG_KEXEC_CORE > > -void smp_send_crash_stop(void) > > +void crash_smp_send_stop(void) > > { > > + static int cpus_stopped; > > cpumask_t mask; > > unsigned long timeout; > > > > + /* > > + * This function can be called twice in panic path, but obviously > > + * we execute this only once. > > + */ > > + if (cpus_stopped) > > + return; > > + > > + cpus_stopped = 1; > > + > This cpus_stopped=1 can't happen on multiple CPUs at the same time as any second > call is guaranteed to be on the same CPU, both are behind panic()s > 'atomic_cmpxchg()'. 'cpu_stopped' variable is not for the race of multi CPUs. This variable is simply to prevent from calling 'smp_cross_call(&mask, IPI_CPU_CRASH_STOP)' twice in the machine_crash_shutdown(). Please look at following call path. * crash_kexec_post_notifiers : true panic() crash_smp_send_stop() { ... cpu_stopped = 1 <= make it '1' smp_cross_call() <= save crash dump for nonpanic cores } __crash_kexec() machine_crash_shutdown() crash_smp_send_stop() { if (cpu_stopped) return <= just return. } > > > Other than my '/proc/vmcore is not available' question above, this looks fine to me: > Reviewed-by: James Morse <james.morse@arm.com> > Tested-by: James Morse <james.morse@arm.com> > > > Thanks! > > James > > >
diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h index 55f08c5..f82b447 100644 --- a/arch/arm64/include/asm/smp.h +++ b/arch/arm64/include/asm/smp.h @@ -148,7 +148,7 @@ static inline void cpu_panic_kernel(void) */ bool cpus_are_stuck_in_kernel(void); -extern void smp_send_crash_stop(void); +extern void crash_smp_send_stop(void); extern bool smp_crash_stop_failed(void); #endif /* ifndef __ASSEMBLY__ */ diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c index 481f54a..11121f6 100644 --- a/arch/arm64/kernel/machine_kexec.c +++ b/arch/arm64/kernel/machine_kexec.c @@ -252,7 +252,7 @@ void machine_crash_shutdown(struct pt_regs *regs) local_irq_disable(); /* shutdown non-crashing cpus */ - smp_send_crash_stop(); + crash_smp_send_stop(); /* for crashing cpu */ crash_save_cpu(regs, smp_processor_id()); diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index dc66e6e..73d8f5e 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -977,11 +977,21 @@ void smp_send_stop(void) } #ifdef CONFIG_KEXEC_CORE -void smp_send_crash_stop(void) +void crash_smp_send_stop(void) { + static int cpus_stopped; cpumask_t mask; unsigned long timeout; + /* + * This function can be called twice in panic path, but obviously + * we execute this only once. + */ + if (cpus_stopped) + return; + + cpus_stopped = 1; + if (num_online_cpus() == 1) return;
Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly version in panic path) introduced crash_smp_send_stop() which is a weak function and can be overriden by architecture codes to fix the side effect caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_ notifiers" option). ARM64 architecture uses the weak version function and the problem is that the weak function simply calls smp_send_stop() which makes other CPUs offline and takes away the chance to save crash information for nonpanic CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel option is enabled. Calling smp_send_crash_stop() in machine_crash_shutdown() is useless because all nonpanic CPUs are already offline by smp_send_stop() in this case and smp_send_crash_stop() only works against online CPUs. The result is that /proc/vmcore is not available with the error messages; "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized". crash_smp_send_stop() is implemented to fix this problem by replacing the exising smp_send_crash_stop() and adding a check for multiple calling to the function. The function (strong symbol version) saves crash information for nonpanic CPUs and machine_crash_shutdown() tries to save crash information for nonpanic CPUs only when crash_kexec_post_notifiers kernel option is disabled. * crash_kexec_post_notifiers : false panic() __crash_kexec() machine_crash_shutdown() crash_smp_send_stop() <= save crash dump for nonpanic cores * crash_kexec_post_notifiers : true panic() crash_smp_send_stop() <= save crash dump for nonpanic cores __crash_kexec() machine_crash_shutdown() crash_smp_send_stop() <= just return. Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com> --- v2: - replace the existing smp_send_crash_stop() with crash_smp_send_stop() and adding called-twice logic to it. - modify the commit message arch/arm64/include/asm/smp.h | 2 +- arch/arm64/kernel/machine_kexec.c | 2 +- arch/arm64/kernel/smp.c | 12 +++++++++++- 3 files changed, 13 insertions(+), 3 deletions(-)