[PATCH -next] perf/core: fix unlock balance in perf_init_event

[PATCH -next] perf/core: fix unlock balance in perf_init_event

[Qian Cai]

The -next commit "perf/core: Optimize perf_init_event()" [1] introduced
an unlock imbalance in perf_init_event() where it calls "goto again" and
then only repeat rcu_read_unlock().

  WARNING: bad unlock balance detected!
  perf_event_open/6185 is trying to release lock (rcu_read_lock) at:
  [<ffffffffb5eb4039>] perf_event_alloc+0xbb9/0x17f0
  but there are no more locks to release!
  other info that might help us debug this:
  2 locks held by perf_event_open/6185:
  #0: ffff888526780b50 (&sig->cred_guard_mutex){+.+.}, at: __do_sys_perf_event_open+0x6ee/0x1460
  #1: ffffffffb866b4e8 (&pmus_srcu){....}, at: perf_event_alloc+0xab8/0x17f0
  Call Trace:
   dump_stack+0xa0/0xea
   print_unlock_imbalance_bug.cold.40+0xb1/0xb6
   lock_release+0x349/0x4b0
   perf_event_alloc+0xbcf/0x17f0
   __do_sys_perf_event_open+0x1e2/0x1460
   __x64_sys_perf_event_open+0x62/0x70
   do_syscall_64+0xcc/0xaec
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

[1] https://lore.kernel.org/lkml/20191022092307.425783389@infradead.org/

Signed-off-by: Qian Cai <cai@lca.pw>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index cfd89b4a02d8..8226d6ecdb86 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10307,7 +10307,6 @@ static struct pmu *perf_init_event(struct perf_event *event)
 			goto unlock;
 	}
 
-	rcu_read_lock();
 	/*
 	 * PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE
 	 * are often aliases for PERF_TYPE_RAW.
@@ -10317,6 +10316,7 @@ static struct pmu *perf_init_event(struct perf_event *event)
 		type = PERF_TYPE_RAW;
 
 again:
+	rcu_read_lock();
 	pmu = idr_find(&pmu_idr, type);
 	rcu_read_unlock();
 	if (pmu) {
-- 
2.21.0 (Apple Git-122)

Re: [PATCH -next] perf/core: fix unlock balance in perf_init_event

[Peter Zijlstra]

On Wed, Nov 06, 2019 at 12:29:35AM -0500, Qian Cai wrote:
> The -next commit "perf/core: Optimize perf_init_event()" [1] introduced
> an unlock imbalance in perf_init_event() where it calls "goto again" and
> then only repeat rcu_read_unlock().
> 
>   WARNING: bad unlock balance detected!
>   perf_event_open/6185 is trying to release lock (rcu_read_lock) at:
>   [<ffffffffb5eb4039>] perf_event_alloc+0xbb9/0x17f0
>   but there are no more locks to release!
>   other info that might help us debug this:
>   2 locks held by perf_event_open/6185:
>   #0: ffff888526780b50 (&sig->cred_guard_mutex){+.+.}, at: __do_sys_perf_event_open+0x6ee/0x1460
>   #1: ffffffffb866b4e8 (&pmus_srcu){....}, at: perf_event_alloc+0xab8/0x17f0
>   Call Trace:
>    dump_stack+0xa0/0xea
>    print_unlock_imbalance_bug.cold.40+0xb1/0xb6
>    lock_release+0x349/0x4b0
>    perf_event_alloc+0xbcf/0x17f0
>    __do_sys_perf_event_open+0x1e2/0x1460
>    __x64_sys_perf_event_open+0x62/0x70
>    do_syscall_64+0xcc/0xaec
>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> [1] https://lore.kernel.org/lkml/20191022092307.425783389@infradead.org/

You wanted to write:

Fixes: 66d258c5b048 ("perf/core: Optimize perf_init_event()")

instead, right? Fixed that for you.

> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>  kernel/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index cfd89b4a02d8..8226d6ecdb86 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -10307,7 +10307,6 @@ static struct pmu *perf_init_event(struct perf_event *event)
>  			goto unlock;
>  	}
>  
> -	rcu_read_lock();
>  	/*
>  	 * PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE
>  	 * are often aliases for PERF_TYPE_RAW.
> @@ -10317,6 +10316,7 @@ static struct pmu *perf_init_event(struct perf_event *event)
>  		type = PERF_TYPE_RAW;
>  
>  again:
> +	rcu_read_lock();
>  	pmu = idr_find(&pmu_idr, type);
>  	rcu_read_unlock();
>  	if (pmu) {
> -- 
> 2.21.0 (Apple Git-122)
> 

Re: [PATCH -next] perf/core: fix unlock balance in perf_init_event

[Qian Cai]

> On Nov 6, 2019, at 4:23 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> You wanted to write:
> 
> Fixes: 66d258c5b048 ("perf/core: Optimize perf_init_event()")
> 
> instead, right? Fixed that for you.

I was not too sure about if the hashes are stable for commits only in the -tip tree. If they remain the same even after merged into the mainline, and then yes.

Re: [PATCH -next] perf/core: fix unlock balance in perf_init_event

[Peter Zijlstra]

On Wed, Nov 06, 2019 at 05:37:34AM -0500, Qian Cai wrote:
> 
> 
> > On Nov 6, 2019, at 4:23 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > You wanted to write:
> > 
> > Fixes: 66d258c5b048 ("perf/core: Optimize perf_init_event()")
> > 
> > instead, right? Fixed that for you.
> 
> I was not too sure about if the hashes are stable for commits only in
> the -tip tree. If they remain the same even after merged into the
> mainline, and then yes.

-tip commits are generally stable.

[tip: perf/core] perf/core: Fix unlock balance in perf_init_event()

[tip-bot2 for Qian Cai]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     deb0c3c29d552ab81ecd5481bb83bf2f4e41927d
Gitweb:        https://git.kernel.org/tip/deb0c3c29d552ab81ecd5481bb83bf2f4e41927d
Author:        Qian Cai <cai@lca.pw>
AuthorDate:    Wed, 06 Nov 2019 00:29:35 -05:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 13 Nov 2019 11:06:13 +01:00

perf/core: Fix unlock balance in perf_init_event()

Commit:

  66d258c5b048 ("perf/core: Optimize perf_init_event()")

introduced an unlock imbalance in perf_init_event() where it calls
"goto again" and then only repeat rcu_read_unlock().

Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 66d258c5b048 ("perf/core: Optimize perf_init_event()")
Link: https://lkml.kernel.org/r/20191106052935.8352-1-cai@lca.pw
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6cb6d68..8d65e03 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10307,7 +10307,6 @@ static struct pmu *perf_init_event(struct perf_event *event)
 			goto unlock;
 	}
 
-	rcu_read_lock();
 	/*
 	 * PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE
 	 * are often aliases for PERF_TYPE_RAW.
@@ -10317,6 +10316,7 @@ static struct pmu *perf_init_event(struct perf_event *event)
 		type = PERF_TYPE_RAW;
 
 again:
+	rcu_read_lock();
 	pmu = idr_find(&pmu_idr, type);
 	rcu_read_unlock();
 	if (pmu) {