diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/events/core.c | 41 |
1 files changed, 33 insertions, 8 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 81aa3a4ece9f..1a3bf48743ce 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -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); } |