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158 lines
4.7 KiB
Diff
158 lines
4.7 KiB
Diff
From 857ea07fb0096e0964ced18ad85a1d9591562114 Mon Sep 17 00:00:00 2001
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From: Peter Zijlstra <peterz@infradead.org>
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Date: Wed, 11 Jan 2017 21:09:50 +0100
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Subject: [PATCH] perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race
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commit 321027c1fe77f892f4ea07846aeae08cefbbb290 upstream.
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commit fe525a280e8b5f04c7666fe22d1a4ef592f7b953 in 3.16.40
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bug: 37901413
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Di Shen reported a race between two concurrent sys_perf_event_open()
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calls where both try and move the same pre-existing software group
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into a hardware context.
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The problem is exactly that described in commit:
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f63a8daa5812 ("perf: Fix event->ctx locking")
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... where, while we wait for a ctx->mutex acquisition, the event->ctx
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relation can have changed under us.
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That very same commit failed to recognise sys_perf_event_context() as an
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external access vector to the events and thereby didn't apply the
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established locking rules correctly.
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So while one sys_perf_event_open() call is stuck waiting on
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mutex_lock_double(), the other (which owns said locks) moves the group
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about. So by the time the former sys_perf_event_open() acquires the
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locks, the context we've acquired is stale (and possibly dead).
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Apply the established locking rules as per perf_event_ctx_lock_nested()
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to the mutex_lock_double() for the 'move_group' case. This obviously means
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we need to validate state after we acquire the locks.
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Reported-by: Di Shen (Keen Lab)
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Tested-by: John Dias <joaodias@google.com>
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Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
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Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
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Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
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Cc: Jiri Olsa <jolsa@redhat.com>
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Cc: Kees Cook <keescook@chromium.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Min Chong <mchong@google.com>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Stephane Eranian <eranian@google.com>
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Cc: Vince Weaver <vincent.weaver@maine.edu>
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Fixes: f63a8daa5812 ("perf: Fix event->ctx locking")
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Link: http://lkml.kernel.org/r/20170106131444.GZ3174@twins.programming.kicks-ass.net
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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[bwh: Backported to 3.16:
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- Use ACCESS_ONCE() instead of READ_ONCE()
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- Test perf_event::group_flags instead of group_caps
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- Add the err_locked cleanup block, which we didn't need before
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- Adjust context]
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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Signed-off-by: Suren Baghdasaryan <surenb@google.com>
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---
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diff --git a/kernel/events/core.c b/kernel/events/core.c
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index 1a0530f..1c53a5c 100644
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--- a/kernel/events/core.c
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+++ b/kernel/events/core.c
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@@ -7440,6 +7440,37 @@
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mutex_lock_nested(b, SINGLE_DEPTH_NESTING);
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}
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+/*
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+ * Variation on perf_event_ctx_lock_nested(), except we take two context
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+ * mutexes.
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+ */
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+static struct perf_event_context *
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+__perf_event_ctx_lock_double(struct perf_event *group_leader,
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+ struct perf_event_context *ctx)
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+{
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+ struct perf_event_context *gctx;
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+
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+again:
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+ rcu_read_lock();
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+ gctx = ACCESS_ONCE(group_leader->ctx);
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+ if (!atomic_inc_not_zero(&gctx->refcount)) {
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+ rcu_read_unlock();
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+ goto again;
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+ }
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+ rcu_read_unlock();
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+
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+ mutex_lock_double(&gctx->mutex, &ctx->mutex);
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+
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+ if (group_leader->ctx != gctx) {
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+ mutex_unlock(&ctx->mutex);
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+ mutex_unlock(&gctx->mutex);
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+ put_ctx(gctx);
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+ goto again;
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+ }
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+
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+ return gctx;
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+}
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+
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/**
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* sys_perf_event_open - open a performance event, associate it to a task/cpu
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*
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@@ -7656,14 +7687,31 @@
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}
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if (move_group) {
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- gctx = group_leader->ctx;
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+ gctx = __perf_event_ctx_lock_double(group_leader, ctx);
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+
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+ /*
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+ * Check if we raced against another sys_perf_event_open() call
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+ * moving the software group underneath us.
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+ */
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+ if (!(group_leader->group_flags & PERF_GROUP_SOFTWARE)) {
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+ /*
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+ * If someone moved the group out from under us, check
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+ * if this new event wound up on the same ctx, if so
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+ * its the regular !move_group case, otherwise fail.
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+ */
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+ if (gctx != ctx) {
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+ err = -EINVAL;
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+ goto err_locked;
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+ } else {
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+ perf_event_ctx_unlock(group_leader, gctx);
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+ move_group = 0;
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+ }
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+ }
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/*
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* See perf_event_ctx_lock() for comments on the details
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* of swizzling perf_event::ctx.
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*/
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- mutex_lock_double(&gctx->mutex, &ctx->mutex);
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-
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perf_remove_from_context(group_leader, false);
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/*
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@@ -7704,7 +7752,7 @@
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perf_unpin_context(ctx);
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if (move_group) {
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- mutex_unlock(&gctx->mutex);
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+ perf_event_ctx_unlock(group_leader, gctx);
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put_ctx(gctx);
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}
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mutex_unlock(&ctx->mutex);
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@@ -7733,6 +7781,11 @@
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fd_install(event_fd, event_file);
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return event_fd;
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+err_locked:
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+ if (move_group)
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+ perf_event_ctx_unlock(group_leader, gctx);
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+ mutex_unlock(&ctx->mutex);
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+ fput(event_file);
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err_context:
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perf_unpin_context(ctx);
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put_ctx(ctx);
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