lkml.org 
[lkml]   [2014]   [Nov]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 3.13 139/162] futex: Fix a race condition between REQUEUE_PI and task death
Date
3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Brian Silverman <bsilver16384@gmail.com>

commit 30a6b8031fe14031ab27c1fa3483cb9780e7f63c upstream.

free_pi_state and exit_pi_state_list both clean up futex_pi_state's.
exit_pi_state_list takes the hb lock first, and most callers of
free_pi_state do too. requeue_pi doesn't, which means free_pi_state
can free the pi_state out from under exit_pi_state_list. For example:

task A | task B
exit_pi_state_list |
pi_state = |
curr->pi_state_list->next |
| futex_requeue(requeue_pi=1)
| // pi_state is the same as
| // the one in task A
| free_pi_state(pi_state)
| list_del_init(&pi_state->list)
| kfree(pi_state)
list_del_init(&pi_state->list) |

Move the free_pi_state calls in requeue_pi to before it drops the hb
locks which it's already holding.

[ tglx: Removed a pointless free_pi_state() call and the hb->lock held
debugging. The latter comes via a seperate patch ]

Signed-off-by: Brian Silverman <bsilver16384@gmail.com>
Cc: austin.linux@gmail.com
Cc: darren@dvhart.com
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/1414282837-23092-1-git-send-email-bsilver16384@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
kernel/futex.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 2b1583e..7947e4c 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -492,8 +492,14 @@ static struct futex_pi_state * alloc_pi_state(void)
return pi_state;
}

+/*
+ * Must be called with the hb lock held.
+ */
static void free_pi_state(struct futex_pi_state *pi_state)
{
+ if (!pi_state)
+ return;
+
if (!atomic_dec_and_test(&pi_state->refcount))
return;

@@ -1407,15 +1413,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
}

retry:
- if (pi_state != NULL) {
- /*
- * We will have to lookup the pi_state again, so free this one
- * to keep the accounting correct.
- */
- free_pi_state(pi_state);
- pi_state = NULL;
- }
-
ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
if (unlikely(ret != 0))
goto out;
@@ -1503,6 +1500,8 @@ retry_private:
case 0:
break;
case -EFAULT:
+ free_pi_state(pi_state);
+ pi_state = NULL;
double_unlock_hb(hb1, hb2);
put_futex_key(&key2);
put_futex_key(&key1);
@@ -1512,6 +1511,8 @@ retry_private:
goto out;
case -EAGAIN:
/* The owner was exiting, try again. */
+ free_pi_state(pi_state);
+ pi_state = NULL;
double_unlock_hb(hb1, hb2);
put_futex_key(&key2);
put_futex_key(&key1);
@@ -1588,6 +1589,7 @@ retry_private:
}

out_unlock:
+ free_pi_state(pi_state);
double_unlock_hb(hb1, hb2);

/*
@@ -1604,8 +1606,6 @@ out_put_keys:
out_put_key1:
put_futex_key(&key1);
out:
- if (pi_state != NULL)
- free_pi_state(pi_state);
return ret ? ret : task_count;
}

--
1.9.1


\
 
 \ /
  Last update: 2014-11-07 00:41    [W:0.380 / U:0.112 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site