[lkml]   [2015]   [Feb]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 1/1] 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 <>
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)) {
return -EPERM;

 \ /
  Last update: 2015-02-02 15:21    [W:0.126 / U:1.828 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site