Commit-ID: f73e22ab450140830005581c2c7ec389791a1b8d Gitweb: http://git.kernel.org/tip/f73e22ab450140830005581c2c7ec389791a1b8d Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Wed, 9 Sep 2015 20:48:22 +0200 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Fri, 18 Sep 2015 09:20:26 +0200 perf: Fix races in computing the header sizes There are two races with the current code: - Another event can join the group and compute a larger header_size concurrently, if the smaller store wins we'll have an incorrect header_size set. - We compute the header_size after the event becomes active, therefore its possible to use the size before its computed. Remedy the first by moving the computation inside the ctx::mutex lock, and the second by placing it _before_ perf_install_in_context(). Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: linux-kernel@xxxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- kernel/events/core.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index dbb5329..b11756f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8399,6 +8399,15 @@ SYSCALL_DEFINE5(perf_event_open, put_ctx(gctx); } + /* + * Precalculate sample_data sizes; do while holding ctx::mutex such + * that we're serialized against further additions and before + * perf_install_in_context() which is the point the event is active and + * can use these values. + */ + perf_event__header_size(event); + perf_event__id_header_size(event); + perf_install_in_context(ctx, event, event->cpu); perf_unpin_context(ctx); @@ -8415,12 +8424,6 @@ SYSCALL_DEFINE5(perf_event_open, mutex_unlock(¤t->perf_event_mutex); /* - * Precalculate sample_data sizes - */ - perf_event__header_size(event); - perf_event__id_header_size(event); - - /* * Drop the reference on the group_event after placing the * new event on the sibling_list. This ensures destruction * of the group leader will find the pointer to itself in -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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