| Message ID | 321e4c16-aa14-beee-b6dc-36e19e5ec35a@huawei.com |
|---|---|
| State | Superseded |
| Headers | show |
On 2017/7/9 16:30, Ding Tianhong wrote: > When enable preempt and debug ftrace, and perform the following steps, the > system will hang: > mount -t debugfs nodev /sys/kernel/debug/ > cd /sys/kernel/debug/tracing/ > echo function_graph > current_tracer > > This is because tracing the preempt_disable/enable calls would cause > trace_clock() which would get local timer to go into infinite recursion > when enable the arch timer erratum workaround for some chips, so Prevent > tracing of preempt_disable/enable() in arch_timer_reg_read_stable(). > > This problem is similar to the fixed by upstream commit 96b3d28bf4 > ("sched/clock: Prevent tracing recursion in sched_clock_cpu()"). > > Fixes: 6acc71ccac71 ("arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs") > Signed-off-by: Ding Tianhong <dingtianhong@huawei.com> > --- > arch/arm64/include/asm/arch_timer.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h > index 74d08e4..67bb7a4 100644 > --- a/arch/arm64/include/asm/arch_timer.h > +++ b/arch/arm64/include/asm/arch_timer.h > @@ -65,13 +65,13 @@ struct arch_timer_erratum_workaround { > u64 _val; \ > if (needs_unstable_timer_counter_workaround()) { \ > const struct arch_timer_erratum_workaround *wa; \ > - preempt_disable(); \ > + preempt_disable_notrace(); \ > wa = __this_cpu_read(timer_unstable_counter_workaround); \ > if (wa && wa->read_##reg) \ > _val = wa->read_##reg(); \ > else \ > _val = read_sysreg(reg); \ > - preempt_enable(); \ > + preempt_enable_notrace(); \ > } else { \ > _val = read_sysreg(reg); \ > } \ This fixes my system hang issue when I using function tracer with enabled timer errata on D03, Tested-by: Hanjun Guo <hanjun.guo@linaro.org> Thanks Hanjun
On Sun, Jul 09, 2017 at 04:30:54PM +0800, Ding Tianhong wrote: > When enable preempt and debug ftrace, and perform the following steps, the > system will hang: > mount -t debugfs nodev /sys/kernel/debug/ > cd /sys/kernel/debug/tracing/ > echo function_graph > current_tracer > > This is because tracing the preempt_disable/enable calls would cause > trace_clock() which would get local timer to go into infinite recursion > when enable the arch timer erratum workaround for some chips, so Prevent > tracing of preempt_disable/enable() in arch_timer_reg_read_stable(). > > This problem is similar to the fixed by upstream commit 96b3d28bf4 > ("sched/clock: Prevent tracing recursion in sched_clock_cpu()"). As I mentioned before, the patch itself looks fine to me, but the commit message is somewhat difficult to read. Can we please change this to: arm64: arch_timer: avoid infinite recursion when ftrace is enabled On platforms with an arch timer erratum workaround, it's possible for arch_timer_reg_read_stable() to recurse into itself when certain tracing options are enabled, leading to stack overflows and related problems. For example, when PREEMPT_TRACER and FUNCTION_GRAPH_TRACER are selected, it's possible to trigger this with: $ mount -t debugfs nodev /sys/kernel/debug/ $ echo function_graph > /sys/kernel/debug/tracing/current_tracer The problem is that in such cases, preempt_disable() instrumentation attempts to acquire a timestamp via trace_clock(), resulting in a call back to arch_timer_reg_read_stable(), and hence recursion. This patch changes arch_timer_reg_read_stable() to use preempt_{disable,enable}_notrace(), which avoids this. With that commit message: Acked-by: Mark Rutland <mark.rutland@arm.com> Daniel, Thomas, would you be happy to fold that in when picking this? Or would you prefer that I fix this up and resend? Thanks, Mark. > Fixes: 6acc71ccac71 ("arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs") > Signed-off-by: Ding Tianhong <dingtianhong@huawei.com> > --- > arch/arm64/include/asm/arch_timer.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h > index 74d08e4..67bb7a4 100644 > --- a/arch/arm64/include/asm/arch_timer.h > +++ b/arch/arm64/include/asm/arch_timer.h > @@ -65,13 +65,13 @@ struct arch_timer_erratum_workaround { > u64 _val; \ > if (needs_unstable_timer_counter_workaround()) { \ > const struct arch_timer_erratum_workaround *wa; \ > - preempt_disable(); \ > + preempt_disable_notrace(); \ > wa = __this_cpu_read(timer_unstable_counter_workaround); \ > if (wa && wa->read_##reg) \ > _val = wa->read_##reg(); \ > else \ > _val = read_sysreg(reg); \ > - preempt_enable(); \ > + preempt_enable_notrace(); \ > } else { \ > _val = read_sysreg(reg); \ > } \ > -- > 1.9.0 > >
On 10/07/17 12:22, Mark Rutland wrote: > On Sun, Jul 09, 2017 at 04:30:54PM +0800, Ding Tianhong wrote: >> When enable preempt and debug ftrace, and perform the following steps, the >> system will hang: >> mount -t debugfs nodev /sys/kernel/debug/ >> cd /sys/kernel/debug/tracing/ >> echo function_graph > current_tracer >> >> This is because tracing the preempt_disable/enable calls would cause >> trace_clock() which would get local timer to go into infinite recursion >> when enable the arch timer erratum workaround for some chips, so Prevent >> tracing of preempt_disable/enable() in arch_timer_reg_read_stable(). >> >> This problem is similar to the fixed by upstream commit 96b3d28bf4 >> ("sched/clock: Prevent tracing recursion in sched_clock_cpu()"). > > As I mentioned before, the patch itself looks fine to me, but the commit > message is somewhat difficult to read. > > Can we please change this to: > > arm64: arch_timer: avoid infinite recursion when ftrace is enabled > > On platforms with an arch timer erratum workaround, it's possible for > arch_timer_reg_read_stable() to recurse into itself when certain > tracing options are enabled, leading to stack overflows and related > problems. > > For example, when PREEMPT_TRACER and FUNCTION_GRAPH_TRACER are > selected, it's possible to trigger this with: > > $ mount -t debugfs nodev /sys/kernel/debug/ > $ echo function_graph > /sys/kernel/debug/tracing/current_tracer > > The problem is that in such cases, preempt_disable() instrumentation > attempts to acquire a timestamp via trace_clock(), resulting in a call > back to arch_timer_reg_read_stable(), and hence recursion. > > This patch changes arch_timer_reg_read_stable() to use > preempt_{disable,enable}_notrace(), which avoids this. > > With that commit message: > > Acked-by: Mark Rutland <mark.rutland@arm.com> > > Daniel, Thomas, would you be happy to fold that in when picking this? Or > would you prefer that I fix this up and resend? With the proposed changes: Acked-by: Marc Zyngier <marc.zyngier@arm.com> M. -- Jazz is not dead. It just smells funny...
On 2017/7/10 19:22, Mark Rutland wrote: > On Sun, Jul 09, 2017 at 04:30:54PM +0800, Ding Tianhong wrote: >> When enable preempt and debug ftrace, and perform the following steps, the >> system will hang: >> mount -t debugfs nodev /sys/kernel/debug/ >> cd /sys/kernel/debug/tracing/ >> echo function_graph > current_tracer >> >> This is because tracing the preempt_disable/enable calls would cause >> trace_clock() which would get local timer to go into infinite recursion >> when enable the arch timer erratum workaround for some chips, so Prevent >> tracing of preempt_disable/enable() in arch_timer_reg_read_stable(). >> >> This problem is similar to the fixed by upstream commit 96b3d28bf4 >> ("sched/clock: Prevent tracing recursion in sched_clock_cpu()"). > > As I mentioned before, the patch itself looks fine to me, but the commit > message is somewhat difficult to read. > > Can we please change this to: > > arm64: arch_timer: avoid infinite recursion when ftrace is enabled > > On platforms with an arch timer erratum workaround, it's possible for > arch_timer_reg_read_stable() to recurse into itself when certain > tracing options are enabled, leading to stack overflows and related > problems. > > For example, when PREEMPT_TRACER and FUNCTION_GRAPH_TRACER are > selected, it's possible to trigger this with: > > $ mount -t debugfs nodev /sys/kernel/debug/ > $ echo function_graph > /sys/kernel/debug/tracing/current_tracer > > The problem is that in such cases, preempt_disable() instrumentation > attempts to acquire a timestamp via trace_clock(), resulting in a call > back to arch_timer_reg_read_stable(), and hence recursion. > > This patch changes arch_timer_reg_read_stable() to use > preempt_{disable,enable}_notrace(), which avoids this. > > With that commit message: > > Acked-by: Mark Rutland <mark.rutland@arm.com> > > Daniel, Thomas, would you be happy to fold that in when picking this? Or > would you prefer that I fix this up and resend? > Hi Danial, Thomas: It looks didn't merge to the mainline tree yet, should I update the commit and resend this patch again? Thanks Ding > Thanks, > Mark. > >> Fixes: 6acc71ccac71 ("arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs") >> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com> >> --- >> arch/arm64/include/asm/arch_timer.h | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h >> index 74d08e4..67bb7a4 100644 >> --- a/arch/arm64/include/asm/arch_timer.h >> +++ b/arch/arm64/include/asm/arch_timer.h >> @@ -65,13 +65,13 @@ struct arch_timer_erratum_workaround { >> u64 _val; \ >> if (needs_unstable_timer_counter_workaround()) { \ >> const struct arch_timer_erratum_workaround *wa; \ >> - preempt_disable(); \ >> + preempt_disable_notrace(); \ >> wa = __this_cpu_read(timer_unstable_counter_workaround); \ >> if (wa && wa->read_##reg) \ >> _val = wa->read_##reg(); \ >> else \ >> _val = read_sysreg(reg); \ >> - preempt_enable(); \ >> + preempt_enable_notrace(); \ >> } else { \ >> _val = read_sysreg(reg); \ >> } \ >> -- >> 1.9.0 >> >> > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > . >
diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h index 74d08e4..67bb7a4 100644 --- a/arch/arm64/include/asm/arch_timer.h +++ b/arch/arm64/include/asm/arch_timer.h @@ -65,13 +65,13 @@ struct arch_timer_erratum_workaround { u64 _val; \ if (needs_unstable_timer_counter_workaround()) { \ const struct arch_timer_erratum_workaround *wa; \ - preempt_disable(); \ + preempt_disable_notrace(); \ wa = __this_cpu_read(timer_unstable_counter_workaround); \ if (wa && wa->read_##reg) \ _val = wa->read_##reg(); \ else \ _val = read_sysreg(reg); \ - preempt_enable(); \ + preempt_enable_notrace(); \ } else { \ _val = read_sysreg(reg); \ } \
When enable preempt and debug ftrace, and perform the following steps, the system will hang: mount -t debugfs nodev /sys/kernel/debug/ cd /sys/kernel/debug/tracing/ echo function_graph > current_tracer This is because tracing the preempt_disable/enable calls would cause trace_clock() which would get local timer to go into infinite recursion when enable the arch timer erratum workaround for some chips, so Prevent tracing of preempt_disable/enable() in arch_timer_reg_read_stable(). This problem is similar to the fixed by upstream commit 96b3d28bf4 ("sched/clock: Prevent tracing recursion in sched_clock_cpu()"). Fixes: 6acc71ccac71 ("arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs") Signed-off-by: Ding Tianhong <dingtianhong@huawei.com> --- arch/arm64/include/asm/arch_timer.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 1.9.0