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drivers/perf: riscv: Do not update the event data if uptodate

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In case of an counter overflow, the event data may get corrupted
if called from an external overflow handler. This happens because
we can't update the counter without starting it when SBI PMU
extension is in use. However, the prev_count has been already
updated at the first pass while the counter value is still the
old one.

The solution is simple where we don't need to update it again
if it is already updated which can be detected using hwc state.
The event state in the overflow handler is updated in the following
patch. Thus, this fix can't be backported to kernel version where
overflow support was added.

Fixes: a8625217a0 ("drivers/perf: riscv: Implement SBI PMU snapshot function")

Closes:https://lore.kernel.org/all/CC51D53B-846C-4D81-86FC-FBF969D0A0D6@pku.edu.cn/

Reported-by: garthlei@pku.edu.cn
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240628-misc_perf_fixes-v4-1-e01cfddcf035@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Atish Patra 2024-06-28 00:51:41 -07:00 committed by Palmer Dabbelt
parent 1613e604df
commit a3f24e83d1
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1 changed files with 1 additions and 1 deletions
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2
drivers/perf/riscv_pmu.c
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@ -167,7 +167,7 @@ u64 riscv_pmu_event_update(struct perf_event *event)
unsigned long cmask;
u64 oldval, delta;
if (!rvpmu->ctr_read)
if (!rvpmu->ctr_read || (hwc->state & PERF_HES_UPTODATE))
return 0;
cmask = riscv_pmu_ctr_get_width_mask(event);