From a21294644623ee41034db60e93aaebed4db0e57b Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 2 Feb 2015 15:05:36 +0100 Subject: [PATCH] locking/futex: Check PF_KTHREAD rather than !p->mm to filter out kthreads attach_to_pi_owner() checks p->mm to prevent attaching to kthreads and this looks doubly wrong: 1. It should actually check PF_KTHREAD, kthread can do use_mm(). 2. If this task is not kthread and it is actually the lock owner we can wrongly return -EPERM instead of -ESRCH or retry-if-EAGAIN. And note that this wrong EPERM is the likely case unless the exiting task is (auto)reaped quickly, we check ->mm before PF_EXITING. Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Cc: Catalin Marinas Cc: Darren Hart Cc: Davidlohr Bueso Cc: Jerome Marchand Cc: Larry Woodman Cc: Linus Torvalds Cc: Mateusz Guzik Link: http://lkml.kernel.org/r/20150202140536.GA26406@redhat.com Signed-off-by: Ingo Molnar --- kernel/futex.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/futex.c b/kernel/futex.c index 4eeb63de7e54..1f6d646eee4a 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -900,7 +900,7 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key, if (!p) return -ESRCH; - if (!p->mm) { + if (unlikely(p->flags & PF_KTHREAD)) { put_task_struct(p); return -EPERM; } -- 2.30.2