* [PATCH] powerpc/perf: Fix book3s kernel to userspace backtraces
@ 2015-05-26 5:10 Anton Blanchard
2015-05-26 8:50 ` Laurentiu Tudor
2015-05-26 23:37 ` Benjamin Herrenschmidt
0 siblings, 2 replies; 4+ messages in thread
From: Anton Blanchard @ 2015-05-26 5:10 UTC (permalink / raw)
To: benh, paulus, mpe; +Cc: linuxppc-dev
When we take a PMU exception or a software event we call
perf_read_regs(). This overloads regs->result with a boolean that
describes if we should use the sampled instruction address register
(SIAR) or the regs.
If the exception is in kernel, we start with the kernel regs and
backtrace through the kernel stack. At this point we switch to the
userspace regs and backtrace the user stack with perf_callchain_user().
Unfortunately these regs have not got the perf_read_regs() treatment,
so regs->result could be anything. If it is non zero,
perf_instruction_pointer() decides to use the SIAR, and we get issues
like this:
0.11% qemu-system-ppc [kernel.kallsyms] [k] _raw_spin_lock_irqsave
|
---_raw_spin_lock_irqsave
|
|--52.35%-- 0
| |
| |--46.39%-- __hrtimer_start_range_ns
| | kvmppc_run_core
| | kvmppc_vcpu_run_hv
| | kvmppc_vcpu_run
| | kvm_arch_vcpu_ioctl_run
| | kvm_vcpu_ioctl
| | do_vfs_ioctl
| | sys_ioctl
| | system_call
| | |
| | |--67.08%-- _raw_spin_lock_irqsave <--- hi mum
| | | |
| | | --100.00%-- 0x7e714
| | | 0x7e714
Notice the bogus _raw_spin_irqsave when we transition from kernel
(system_call) to userspace (0x7e714). We inserted what was in the SIAR.
Add a check in regs_use_siar() to check that the regs in question
are from a PMU exception. With this fix the backtrace makes sense:
0.47% qemu-system-ppc [kernel.vmlinux] [k] _raw_spin_lock_irqsave
|
---_raw_spin_lock_irqsave
|
|--53.83%-- 0
| |
| |--44.73%-- hrtimer_try_to_cancel
| | kvmppc_start_thread
| | kvmppc_run_core
| | kvmppc_vcpu_run_hv
| | kvmppc_vcpu_run
| | kvm_arch_vcpu_ioctl_run
| | kvm_vcpu_ioctl
| | do_vfs_ioctl
| | sys_ioctl
| | system_call
| | __ioctl
| | 0x7e714
| | 0x7e714
Signed-off-by: Anton Blanchard <anton@samba.org>
---
arch/powerpc/perf/core-book3s.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 12b6384..42a3725 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -131,7 +131,10 @@ static void pmao_restore_workaround(bool ebb) { }
static bool regs_use_siar(struct pt_regs *regs)
{
- return !!regs->result;
+ if ((TRAP(regs) == 0xf00) && regs->result)
+ return true;
+
+ return false;
}
/*
--
2.1.4
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] powerpc/perf: Fix book3s kernel to userspace backtraces
2015-05-26 5:10 [PATCH] powerpc/perf: Fix book3s kernel to userspace backtraces Anton Blanchard
@ 2015-05-26 8:50 ` Laurentiu Tudor
2015-05-26 12:09 ` Anton Blanchard
2015-05-26 23:37 ` Benjamin Herrenschmidt
1 sibling, 1 reply; 4+ messages in thread
From: Laurentiu Tudor @ 2015-05-26 8:50 UTC (permalink / raw)
To: Anton Blanchard, benh, paulus, mpe; +Cc: linuxppc-dev
On 05/26/2015 08:10 AM, Anton Blanchard wrote:
> When we take a PMU exception or a software event we call
> perf_read_regs(). This overloads regs->result with a boolean that
> describes if we should use the sampled instruction address register
> (SIAR) or the regs.
>
> If the exception is in kernel, we start with the kernel regs and
> backtrace through the kernel stack. At this point we switch to the
> userspace regs and backtrace the user stack with perf_callchain_user().
>
> Unfortunately these regs have not got the perf_read_regs() treatment,
> so regs->result could be anything. If it is non zero,
> perf_instruction_pointer() decides to use the SIAR, and we get issues
> like this:
>
> 0.11% qemu-system-ppc [kernel.kallsyms] [k] _raw_spin_lock_irqsave
> |
> ---_raw_spin_lock_irqsave
> |
> |--52.35%-- 0
> | |
> | |--46.39%-- __hrtimer_start_range_ns
> | | kvmppc_run_core
> | | kvmppc_vcpu_run_hv
> | | kvmppc_vcpu_run
> | | kvm_arch_vcpu_ioctl_run
> | | kvm_vcpu_ioctl
> | | do_vfs_ioctl
> | | sys_ioctl
> | | system_call
> | | |
> | | |--67.08%-- _raw_spin_lock_irqsave <--- hi mum
> | | | |
> | | | --100.00%-- 0x7e714
> | | | 0x7e714
>
> Notice the bogus _raw_spin_irqsave when we transition from kernel
> (system_call) to userspace (0x7e714). We inserted what was in the SIAR.
>
> Add a check in regs_use_siar() to check that the regs in question
> are from a PMU exception. With this fix the backtrace makes sense:
>
> 0.47% qemu-system-ppc [kernel.vmlinux] [k] _raw_spin_lock_irqsave
> |
> ---_raw_spin_lock_irqsave
> |
> |--53.83%-- 0
> | |
> | |--44.73%-- hrtimer_try_to_cancel
> | | kvmppc_start_thread
> | | kvmppc_run_core
> | | kvmppc_vcpu_run_hv
> | | kvmppc_vcpu_run
> | | kvm_arch_vcpu_ioctl_run
> | | kvm_vcpu_ioctl
> | | do_vfs_ioctl
> | | sys_ioctl
> | | system_call
> | | __ioctl
> | | 0x7e714
> | | 0x7e714
>
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
> arch/powerpc/perf/core-book3s.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 12b6384..42a3725 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -131,7 +131,10 @@ static void pmao_restore_workaround(bool ebb) { }
>
> static bool regs_use_siar(struct pt_regs *regs)
> {
> - return !!regs->result;
> + if ((TRAP(regs) == 0xf00) && regs->result)
> + return true;
> +
> + return false;
Why not just
return (TRAP(regs) == 0xf00) && regs->result;
?
---
Best Regards, Laurentiu;
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] powerpc/perf: Fix book3s kernel to userspace backtraces
2015-05-26 5:10 [PATCH] powerpc/perf: Fix book3s kernel to userspace backtraces Anton Blanchard
2015-05-26 8:50 ` Laurentiu Tudor
@ 2015-05-26 23:37 ` Benjamin Herrenschmidt
1 sibling, 0 replies; 4+ messages in thread
From: Benjamin Herrenschmidt @ 2015-05-26 23:37 UTC (permalink / raw)
To: Anton Blanchard; +Cc: paulus, mpe, linuxppc-dev
On Tue, 2015-05-26 at 15:10 +1000, Anton Blanchard wrote:
> When we take a PMU exception or a software event we call
> perf_read_regs(). This overloads regs->result with a boolean that
> describes if we should use the sampled instruction address register
> (SIAR) or the regs.
>
> If the exception is in kernel, we start with the kernel regs and
> backtrace through the kernel stack. At this point we switch to the
> userspace regs and backtrace the user stack with perf_callchain_user().
>
> Unfortunately these regs have not got the perf_read_regs() treatment,
> so regs->result could be anything. If it is non zero,
> perf_instruction_pointer() decides to use the SIAR, and we get issues
> like this:
CC stable ?
> 0.11% qemu-system-ppc [kernel.kallsyms] [k] _raw_spin_lock_irqsave
> |
> ---_raw_spin_lock_irqsave
> |
> |--52.35%-- 0
> | |
> | |--46.39%-- __hrtimer_start_range_ns
> | | kvmppc_run_core
> | | kvmppc_vcpu_run_hv
> | | kvmppc_vcpu_run
> | | kvm_arch_vcpu_ioctl_run
> | | kvm_vcpu_ioctl
> | | do_vfs_ioctl
> | | sys_ioctl
> | | system_call
> | | |
> | | |--67.08%-- _raw_spin_lock_irqsave <--- hi mum
> | | | |
> | | | --100.00%-- 0x7e714
> | | | 0x7e714
>
> Notice the bogus _raw_spin_irqsave when we transition from kernel
> (system_call) to userspace (0x7e714). We inserted what was in the SIAR.
>
> Add a check in regs_use_siar() to check that the regs in question
> are from a PMU exception. With this fix the backtrace makes sense:
>
> 0.47% qemu-system-ppc [kernel.vmlinux] [k] _raw_spin_lock_irqsave
> |
> ---_raw_spin_lock_irqsave
> |
> |--53.83%-- 0
> | |
> | |--44.73%-- hrtimer_try_to_cancel
> | | kvmppc_start_thread
> | | kvmppc_run_core
> | | kvmppc_vcpu_run_hv
> | | kvmppc_vcpu_run
> | | kvm_arch_vcpu_ioctl_run
> | | kvm_vcpu_ioctl
> | | do_vfs_ioctl
> | | sys_ioctl
> | | system_call
> | | __ioctl
> | | 0x7e714
> | | 0x7e714
>
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
> arch/powerpc/perf/core-book3s.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 12b6384..42a3725 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -131,7 +131,10 @@ static void pmao_restore_workaround(bool ebb) { }
>
> static bool regs_use_siar(struct pt_regs *regs)
> {
> - return !!regs->result;
> + if ((TRAP(regs) == 0xf00) && regs->result)
> + return true;
> +
> + return false;
> }
>
> /*
^ permalink raw reply [flat|nested] 4+ messages in thread
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2015-05-26 5:10 [PATCH] powerpc/perf: Fix book3s kernel to userspace backtraces Anton Blanchard
2015-05-26 8:50 ` Laurentiu Tudor
2015-05-26 12:09 ` Anton Blanchard
2015-05-26 23:37 ` Benjamin Herrenschmidt
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