Commit 8b10c5e2 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar

perf: Annotate inherited event ctx->mutex recursion

While fuzzing Sasha tripped over another ctx->mutex recursion lockdep
splat. Annotate this.
Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 3e0283a5
......@@ -913,10 +913,30 @@ static void put_ctx(struct perf_event_context *ctx)
* Those places that change perf_event::ctx will hold both
* perf_event_ctx::mutex of the 'old' and 'new' ctx value.
*
* Lock ordering is by mutex address. There is one other site where
* perf_event_context::mutex nests and that is put_event(). But remember that
* that is a parent<->child context relation, and migration does not affect
* children, therefore these two orderings should not interact.
* Lock ordering is by mutex address. There are two other sites where
* perf_event_context::mutex nests and those are:
*
* - perf_event_exit_task_context() [ child , 0 ]
* __perf_event_exit_task()
* sync_child_event()
* put_event() [ parent, 1 ]
*
* - perf_event_init_context() [ parent, 0 ]
* inherit_task_group()
* inherit_group()
* inherit_event()
* perf_event_alloc()
* perf_init_event()
* perf_try_init_event() [ child , 1 ]
*
* While it appears there is an obvious deadlock here -- the parent and child
* nesting levels are inverted between the two. This is in fact safe because
* life-time rules separate them. That is an exiting task cannot fork, and a
* spawning task cannot (yet) exit.
*
* But remember that that these are parent<->child context relations, and
* migration does not affect children, therefore these two orderings should not
* interact.
*
* The change in perf_event::ctx does not affect children (as claimed above)
* because the sys_perf_event_open() case will install a new event and break
......@@ -3657,9 +3677,6 @@ static void perf_remove_from_owner(struct perf_event *event)
}
}
/*
* Called when the last reference to the file is gone.
*/
static void put_event(struct perf_event *event)
{
struct perf_event_context *ctx;
......@@ -3697,6 +3714,9 @@ int perf_event_release_kernel(struct perf_event *event)
}
EXPORT_SYMBOL_GPL(perf_event_release_kernel);
/*
* Called when the last reference to the file is gone.
*/
static int perf_release(struct inode *inode, struct file *file)
{
put_event(file->private_data);
......@@ -7364,7 +7384,12 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
return -ENODEV;
if (event->group_leader != event) {
ctx = perf_event_ctx_lock(event->group_leader);
/*
* This ctx->mutex can nest when we're called through
* inheritance. See the perf_event_ctx_lock_nested() comment.
*/
ctx = perf_event_ctx_lock_nested(event->group_leader,
SINGLE_DEPTH_NESTING);
BUG_ON(!ctx);
}
......
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