kernel.git/kernel/futex.c, branch linux-2.6.31.y

futex_lock_pi() key refcnt fix

2010-04-01T22:55:26Z

commit 5ecb01cfdf96c5f465192bdb2a4fd4a61a24c6cc upstream. This fixes a futex key reference count bug in futex_lock_pi(), where a key's reference count is incremented twice but decremented only once, causing the backing object to not be released. If the futex is created in a temporary file in an ext3 file system, this bug causes the file's inode to become an "undead" orphan, which causes an oops from a BUG_ON() in ext3_put_super() when the file system is unmounted. glibc's test suite is known to trigger this, see . The bug is a regression from 2.6.28-git3, namely Peter Zijlstra's 38d47c1b7075bd7ec3881141bb3629da58f88dab "[PATCH] futex: rely on get_user_pages() for shared futexes". That commit made get_futex_key() also increment the reference count of the futex key, and updated its callers to decrement the key's reference count before returning. Unfortunately the normal exit path in futex_lock_pi() wasn't corrected: the reference count is incremented by get_futex_key() and queue_lock(), but the normal exit path only decrements once, via unqueue_me_pi(). The fix is to put_futex_key() after unqueue_me_pi(), since 2.6.31 this is easily done by 'goto out_put_key' rather than 'goto out'. Signed-off-by: Mikael Pettersson Acked-by: Peter Zijlstra Acked-by: Darren Hart Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Handle user space corruption gracefully

2010-04-01T22:55:26Z

commit 51246bfd189064079c54421507236fd2723b18f3 upstream. If the owner of a PI futex dies we fix up the pi_state and set pi_state->owner to NULL. When a malicious or just sloppy programmed user space application sets the futex value to 0 e.g. by calling pthread_mutex_init(), then the futex can be acquired again. A new waiter manages to enqueue itself on the pi_state w/o damage, but on unlock the kernel dereferences pi_state->owner and oopses. Prevent this by checking pi_state->owner in the unlock path. If pi_state->owner is not current we know that user space manipulated the futex value. Ignore the mess and return -EINVAL. This catches the above case and also the case where a task hijacks the futex by setting the tid value and then tries to unlock it. Reported-by: Jermome Marchand Signed-off-by: Thomas Gleixner Acked-by: Darren Hart Acked-by: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman

futex: Handle futex value corruption gracefully

2010-04-01T22:55:26Z

commit 59647b6ac3050dd964bc556fe6ef22f4db5b935c upstream. The WARN_ON in lookup_pi_state which complains about a mismatch between pi_state->owner->pid and the pid which we retrieved from the user space futex is completely bogus. The code just emits the warning and then continues despite the fact that it detected an inconsistent state of the futex. A conveniant way for user space to spam the syslog. Replace the WARN_ON by a consistency check. If the values do not match return -EINVAL and let user space deal with the mess it created. This also fixes the missing task_pid_vnr() when we compare the pi_state->owner pid with the futex value. Reported-by: Jermome Marchand Signed-off-by: Thomas Gleixner Acked-by: Darren Hart Acked-by: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman

futex: Take mmap_sem for get_user_pages in fault_in_user_writeable

2009-12-18T21:43:21Z

commit 722d0172377a5697919b9f7e5beb95165b1dec4e upstream. get_user_pages() must be called with mmap_sem held. Signed-off-by: Andi Kleen Cc: Andrew Morton Cc: Nick Piggin Cc: Darren Hart Cc: Peter Zijlstra LKML-Reference: <20091208121942.GA21298@basil.fritz.box> Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Fix spurious wakeup for requeue_pi really

2009-11-10T00:21:54Z

commit 11df6dddcbc38affb7473aad3d962baf8414a947 upstream. The requeue_pi path doesn't use unqueue_me() (and the racy lock_ptr == NULL test) nor does it use the wake_list of futex_wake() which where the reason for commit 41890f2 (futex: Handle spurious wake up) See debugging discussing on LKML Message-ID: <4AD4080C.20703@us.ibm.com> The changes in this fix to the wait_requeue_pi path were considered to be a likely unecessary, but harmless safety net. But it turns out that due to the fact that for unknown $@#!*( reasons EWOULDBLOCK is defined as EAGAIN we built an endless loop in the code path which returns correctly EWOULDBLOCK. Spurious wakeups in wait_requeue_pi code path are unlikely so we do the easy solution and return EWOULDBLOCK^WEAGAIN to user space and let it deal with the spurious wakeup. Cc: Darren Hart Cc: Peter Zijlstra Cc: Eric Dumazet Cc: John Stultz Cc: Dinakar Guniguntala LKML-Reference: <4AE23C74.1090502@us.ibm.com> Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Move drop_futex_key_refs out of spinlock'ed region

2009-11-10T00:21:53Z

commit 89061d3d58e1f0742139605dc6a7950aa1ecc019 upstream. When requeuing tasks from one futex to another, the reference held by the requeued task to the original futex location needs to be dropped eventually. Dropping the reference may ultimately lead to a call to "iput_final" and subsequently call into filesystem- specific code - which may be non-atomic. It is therefore safer to defer this drop operation until after the futex_hash_bucket spinlock has been dropped. Originally-From: Helge Bahmann Signed-off-by: Darren Hart Cc: Peter Zijlstra Cc: Eric Dumazet Cc: Dinakar Guniguntala Cc: John Stultz Cc: Sven-Thorsten Dietrich Cc: John Kacur LKML-Reference: <4AD7A298.5040802@us.ibm.com> Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

futex: Check for NULL keys in match_futex

2009-11-10T00:21:52Z

commit 2bc872036e1c5948b5b02942810bbdd8dbdb9812 upstream. If userspace tries to perform a requeue_pi on a non-requeue_pi waiter, it will find the futex_q->requeue_pi_key to be NULL and OOPS. Check for NULL in match_futex() instead of doing explicit NULL pointer checks on all call sites. While match_futex(NULL, NULL) returning false is a little odd, it's still correct as we expect valid key references. Signed-off-by: Darren Hart Cc: Peter Zijlstra Cc: Ingo Molnar CC: Eric Dumazet CC: Dinakar Guniguntala CC: John Stultz LKML-Reference: <4AD60687.10306@us.ibm.com> Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Handle spurious wake up

2009-11-10T00:21:51Z

commit d58e6576b0deec6f0b9ff8450fe282da18c50883 upstream. The futex code does not handle spurious wake up in futex_wait and futex_wait_requeue_pi. The code assumes that any wake up which was not caused by futex_wake / requeue or by a timeout was caused by a signal wake up and returns one of the syscall restart error codes. In case of a spurious wake up the signal delivery code which deals with the restart error codes is not invoked and we return that error code to user space. That causes applications which actually check the return codes to fail. Blaise reported that on preempt-rt a python test program run into a exception trap. -rt exposed that due to a built in spurious wake up accelerator :) Solve this by checking signal_pending(current) in the wake up path and handle the spurious wake up case w/o returning to user space. Reported-by: Blaise Gassend Debugged-by: Darren Hart Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman

futex: Fix wakeup race by setting TASK_INTERRUPTIBLE before queue_me()

2009-10-22T22:11:52Z

commit 0729e196147692d84d4c099fcff056eba2ed61d8 upstream. PI futexes do not use the same plist_node_empty() test for wakeup. It was possible for the waiter (in futex_wait_requeue_pi()) to set TASK_INTERRUPTIBLE after the waker assigned the rtmutex to the waiter. The waiter would then note the plist was not empty and call schedule(). The task would not be found by any subsequeuent futex wakeups, resulting in a userspace hang. By moving the setting of TASK_INTERRUPTIBLE to before the call to queue_me(), the race with the waker is eliminated. Since we no longer call get_user() from within queue_me(), there is no need to delay the setting of TASK_INTERRUPTIBLE until after the call to queue_me(). The FUTEX_LOCK_PI operation is not affected as futex_lock_pi() relies entirely on the rtmutex code to handle schedule() and wakeup. The requeue PI code is affected because the waiter starts as a non-PI waiter and is woken on a PI futex. Remove the crusty old comment about holding spinlocks() across get_user() as we no longer do that. Correct the locking statement with a description of why the test is performed. Signed-off-by: Darren Hart Acked-by: Peter Zijlstra Cc: Steven Rostedt Cc: Eric Dumazet Cc: Dinakar Guniguntala Cc: John Stultz LKML-Reference: <20090922053038.8717.97838.stgit@Aeon> Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

futex: Detect mismatched requeue targets

2009-10-22T22:11:52Z

commit 84bc4af59081ee974dd80210e694ab59ebe51ce8 upstream. There is currently no check to ensure that userspace uses the same futex requeue target (uaddr2) in futex_requeue() that the waiter used in futex_wait_requeue_pi(). A mismatch here could very unexpected results as the waiter assumes it either wakes on uaddr1 or uaddr2. We could detect this on wakeup in the waiter, but the cleanup is more intense after the improper requeue has occured. This patch stores the waiter's expected requeue target in a new requeue_pi_key pointer in the futex_q which futex_requeue() checks prior to attempting to do a proxy lock acquistion or a requeue when requeue_pi=1. If they don't match, return -EINVAL from futex_requeue, aborting the requeue of any remaining waiters. Signed-off-by: Darren Hart Cc: Peter Zijlstra Cc: Eric Dumazet Cc: John Kacur Cc: Dinakar Guniguntala Cc: John Stultz LKML-Reference: <20090814003650.14634.63916.stgit@Aeon> Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman