From: Paul <p@1g4.org>
To: acme@kernel.org, namhyung@kernel.org
Cc: peterz@infradead.org, mingo@redhat.com, mark.rutland@arm.com,
alexander.shishkin@linux.intel.com, jolsa@kernel.org,
irogers@google.com, adrian.hunter@intel.com,
james.clark@linaro.org, alexey.budankov@linux.intel.com,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
Paul Moses <p@1g4.org>
Subject: [PATCH] perf record: Skip affinity for per-thread mmap buffers
Date: Fri, 30 Oct 2026 06:59:28 +0000 [thread overview]
Message-ID: <20261030065857.2157899-1-p@1g4.org> (raw)
From: Paul Moses <p@1g4.org>
Per-thread mmap buffers use CPU -1 to mean any CPU. Combining --per-thread
with --affinity=cpu passes this value to __set_bit() when constructing the
reader affinity mask, causing an out-of-bounds bitmap access and SIGSEGV.
Program received signal SIGSEGV, Segmentation fault.
0x0000555555f3488e in mmap.mmap ()
#0 0x0000555555f3488e in mmap.mmap ()
#1 0x0000555555e2f7bf in mmap_per_evsel (evlist=evlist@entry=0x7fffedcc1150, ops=ops@entry=0x7fffffffaf50, idx=idx@entry=0, mp=mp@entry=0x7fffffffaf70, cpu_idx=cpu_idx@entry=0, thread=thread@entry=0, _output=0x7fffffffaf08, _output_overwrite=0x7fffffffaf04, nr_mmaps=0x7fffffffaf0c) at evlist.c:598
#2 0x0000555555e2ef96 in mmap_per_thread (evlist=0x7fffedcc1150, ops=0x7fffffffaf50, mp=0x7fffffffaf70) at evlist.c:650
#3 perf_evlist__mmap_ops (evlist=0x7fffedcc1150, ops=0x7fffffffaf50, mp=0x7fffffffaf70) at evlist.c:748
#4 0x0000555555f2150d in evlist.mmap_ex ()
#5 0x0000555555db0b0a in record.open ()
#6 0x0000555555dadea7 in __cmd_record ()
#7 0x0000555555daca89 in cmd_record ()
#8 0x0000555555e27d53 in run_builtin ()
#9 0x0000555555e277cf in main ()
rip 0x555555f3488e 0x555555f3488e <mmap.mmap+382>
rax 0x7fffef9e9bd0 140737213537232
rbx 0x7fffedd249a0 140737183369632
rcx 0x3ffffffffffffff 288230376151711743
rdx 0x8000000000000000 -9223372036854775808
rsi 0x0 0
rdi 0x7fffef9e9bd0 140737213537232
0x555555f34876 <mmap__mmap+358>: movswq 0x10(%rbx),%rcx
0x555555f3487b <mmap__mmap+363>: mov 0xb8(%rbx),%rax
0x555555f34882 <mmap__mmap+370>: mov $0x1,%edx
0x555555f34887 <mmap__mmap+375>: shl %cl,%rdx
0x555555f3488a <mmap__mmap+378>: shr $0x6,%rcx
=> 0x555555f3488e <mmap__mmap+382>: or %rdx,(%rax,%rcx,8)
0x555555f34892 <mmap__mmap+386>: lea 0x17711b(%rip),%r14 # 0x5555560ab9b4 <verbose>
0x555555f34899 <mmap__mmap+393>: cmpl $0x2,(%r14)
0x555555f3489d <mmap__mmap+397>: jne 0x555555f348f7 <mmap__mmap+487>
0x555555f3489f <mmap__mmap+399>: mov 0xb8(%rbx),%rdi
0x555555f348a6 <mmap__mmap+406>: mov 0xc0(%rbx),%esi
0x555555f348ac <mmap__mmap+412>: lea -0x430(%rbp),%r12
Only construct and apply reader affinity masks for buffers with a
nonnegative CPU. Skip the reader-side bitmap operations as well, since
per-thread buffers no longer allocate an affinity mask.
Fixes: 8384a2600c7d ("perf record: Adapt affinity to machines with #CPUs > 1K")
Signed-off-by: Paul Moses <p@1g4.org>
---
tools/perf/builtin-record.c | 2 +-
tools/perf/util/mmap.c | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index a57987851cf0..d7c8f490cb62 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1565,7 +1565,7 @@ static struct perf_event_header finished_init_event = {
static void record__adjust_affinity(struct record *rec, struct mmap *map)
{
- if (rec->opts.affinity != PERF_AFFINITY_SYS &&
+ if (map->core.cpu.cpu >= 0 && rec->opts.affinity != PERF_AFFINITY_SYS &&
!bitmap_equal(thread->mask->affinity.bits, map->affinity_mask.bits,
thread->mask->affinity.nbits)) {
bitmap_zero(thread->mask->affinity.bits, thread->mask->affinity.nbits);
diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
index 358e70c4f3ed..be3dffdaede8 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -292,8 +292,8 @@ int mmap__mmap(struct mmap *map, struct mmap_params *mp, int fd, struct perf_cpu
return -1;
}
- if (mp->affinity != PERF_AFFINITY_SYS &&
- perf_mmap__setup_affinity_mask(map, mp)) {
+ if (cpu.cpu >= 0 && mp->affinity != PERF_AFFINITY_SYS &&
+ perf_mmap__setup_affinity_mask(map, mp)) {
pr_debug2("failed to alloc mmap affinity mask, error %d\n",
errno);
return -1;
--
2.56.GIT
reply other threads:[~2026-10-30 6:59 UTC|newest]
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