From 366efbff58092fac48421fa34018bb34c326088e Mon Sep 17 00:00:00 2001 From: Ian Rogers Date: Mon, 27 Nov 2023 14:08:14 -0800 Subject: libperf: Lazily allocate/size mmap event copy The event copy in the mmap is used to have storage to read an event. Not all users of mmaps read the events, such as perf record. The amount of buffer was also statically set to PERF_SAMPLE_MAX_SIZE rather than the amount necessary from the header's event size. Switch to a model where the event_copy is reallocated if too small to the event's size. This adds the potential for the event to move, so if a copy of the event pointer were stored it could be broken. All the current users do: while(event = perf_mmap__read_event()) { ... } and so they would be broken due to the event being overwritten if they had stored the pointer. Manual inspection and address sanitizer testing also shows the event pointer not being stored. Signed-off-by: Ian Rogers Acked-by: Namhyung Kim Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Andi Kleen Cc: Athira Jajeev Cc: Changbin Du Cc: Colin Ian King Cc: Dmitrii Dolgov <9erthalion6@gmail.com> Cc: German Gomez Cc: Guilherme Amadio Cc: Huacai Chen Cc: Ingo Molnar Cc: James Clark Cc: Jiri Olsa Cc: K Prateek Nayak Cc: Kajol Jain Cc: Kan Liang Cc: Leo Yan Cc: Li Dong Cc: Liam Howlett Cc: Mark Rutland Cc: Masami Hiramatsu (Google) Cc: Miguel Ojeda Cc: Ming Wang Cc: Nick Terrell Cc: Paolo Bonzini Cc: Peter Zijlstra Cc: Ravi Bangoria Cc: Sandipan Das Cc: Sean Christopherson Cc: Steinar H. Gunderson Cc: Vincent Whitchurch Cc: Wenyu Liu Cc: Yang Jihong Link: https://lore.kernel.org/r/20231127220902.1315692-3-irogers@google.com [ Replace two lines with equivalent zfree(&map->event_copy) ] Signed-off-by: Arnaldo Carvalho de Melo --- tools/lib/perf/include/internal/mmap.h | 3 ++- tools/lib/perf/mmap.c | 20 +++++++++++++++++--- 2 files changed, 19 insertions(+), 4 deletions(-) (limited to 'tools/lib') diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h index 5a062af8e9d8..5f08cab61ece 100644 --- a/tools/lib/perf/include/internal/mmap.h +++ b/tools/lib/perf/include/internal/mmap.h @@ -33,7 +33,8 @@ struct perf_mmap { bool overwrite; u64 flush; libperf_unmap_cb_t unmap_cb; - char event_copy[PERF_SAMPLE_MAX_SIZE] __aligned(8); + void *event_copy; + size_t event_copy_sz; struct perf_mmap *next; }; diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c index 2184814b37dd..0c903c2372c9 100644 --- a/tools/lib/perf/mmap.c +++ b/tools/lib/perf/mmap.c @@ -19,6 +19,7 @@ void perf_mmap__init(struct perf_mmap *map, struct perf_mmap *prev, bool overwrite, libperf_unmap_cb_t unmap_cb) { + /* Assume fields were zero initialized. */ map->fd = -1; map->overwrite = overwrite; map->unmap_cb = unmap_cb; @@ -51,13 +52,18 @@ int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp, void perf_mmap__munmap(struct perf_mmap *map) { - if (map && map->base != NULL) { + if (!map) + return; + + zfree(&map->event_copy); + map->event_copy_sz = 0; + if (map->base) { munmap(map->base, perf_mmap__mmap_len(map)); map->base = NULL; map->fd = -1; refcount_set(&map->refcnt, 0); } - if (map && map->unmap_cb) + if (map->unmap_cb) map->unmap_cb(map); } @@ -223,9 +229,17 @@ static union perf_event *perf_mmap__read(struct perf_mmap *map, */ if ((*startp & map->mask) + size != ((*startp + size) & map->mask)) { unsigned int offset = *startp; - unsigned int len = min(sizeof(*event), size), cpy; + unsigned int len = size, cpy; void *dst = map->event_copy; + if (size > map->event_copy_sz) { + dst = realloc(map->event_copy, size); + if (!dst) + return NULL; + map->event_copy = dst; + map->event_copy_sz = size; + } + do { cpy = min(map->mask + 1 - (offset & map->mask), len); memcpy(dst, &data[offset & map->mask], cpy); -- cgit v1.2.3