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perf: Fix default aux_watermark calculation

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[ Upstream commit 43deb76b19663a96ec2189d8f4eb9a9dc2d7623f ]

The default aux_watermark is half the AUX area buffer size. In general,
on a 64-bit architecture, the AUX area buffer size could be a bigger than
fits in a 32-bit type, but the calculation does not allow for that
possibility.

However the aux_watermark value is recorded in a u32, so should not be
more than U32_MAX either.

Fix by doing the calculation in a correctly sized type, and limiting the
result to U32_MAX.

Fixes: d68e6799a5c8 ("perf: Cap allocation order at aux_watermark")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240624201101.60186-7-adrian.hunter@intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Adrian Hunter 2024-06-24 23:11:00 +03:00 committed by Greg Kroah-Hartman
parent e8bf18de94
commit 9bed6852d3
1 changed files with 3 additions and 1 deletions
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4
kernel/events/ring_buffer.c
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@ -688,7 +688,9 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event,
* max_order, to aid PMU drivers in double buffering.
*/
if (!watermark)
watermark = nr_pages << (PAGE_SHIFT - 1);
watermark = min_t(unsigned long,
U32_MAX,
(unsigned long)nr_pages << (PAGE_SHIFT - 1));
/*
* Use aux_watermark as the basis for chunking to