Messages in this thread Patch in this message | | | Date | Mon, 2 Feb 2015 15:05:36 +0100 | From | Oleg Nesterov <> | Subject | [PATCH 1/1] futex: check PF_KTHREAD rather than !p->mm to filter out kthreads |
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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> --- kernel/futex.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c index 63678b5..b101381 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; } -- 1.5.5.1
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