Messages in this thread Patch in this message | | | Date | Wed, 18 Feb 2015 09:11:20 -0800 | From | tip-bot for Oleg Nesterov <> | Subject | [tip:locking/core] locking/futex: Check PF_KTHREAD rather than !p->mm to filter out kthreads |
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Commit-ID: a21294644623ee41034db60e93aaebed4db0e57b Gitweb: http://git.kernel.org/tip/a21294644623ee41034db60e93aaebed4db0e57b Author: Oleg Nesterov <oleg@redhat.com> AuthorDate: Mon, 2 Feb 2015 15:05:36 +0100 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 18 Feb 2015 16:57:09 +0100
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 <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Darren Hart <darren@dvhart.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: Larry Woodman <lwoodman@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mateusz Guzik <mguzik@redhat.com> Link: http://lkml.kernel.org/r/20150202140536.GA26406@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/futex.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/futex.c b/kernel/futex.c index 4eeb63d..1f6d646 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; }
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