diff options
Diffstat (limited to '0008-futex-avoid-race-between-requeue-and-wake.patch')
| -rw-r--r-- | 0008-futex-avoid-race-between-requeue-and-wake.patch | 94 |
1 files changed, 0 insertions, 94 deletions
diff --git a/0008-futex-avoid-race-between-requeue-and-wake.patch b/0008-futex-avoid-race-between-requeue-and-wake.patch deleted file mode 100644 index 8685e116896d..000000000000 --- a/0008-futex-avoid-race-between-requeue-and-wake.patch +++ /dev/null @@ -1,94 +0,0 @@ -From aafcd8f8692fb9e389608c1efad2e57c0bbb9362 Mon Sep 17 00:00:00 2001 -From: Linus Torvalds <torvalds@linux-foundation.org> -Date: Tue, 8 Apr 2014 15:30:07 -0700 -Subject: [PATCH 08/10] futex: avoid race between requeue and wake - -commit 69cd9eba38867a493a043bb13eb9b33cad5f1a9a upstream. - -Jan Stancek reported: - "pthread_cond_broadcast/4-1.c testcase from openposix testsuite (LTP) - occasionally fails, because some threads fail to wake up. - - Testcase creates 5 threads, which are all waiting on same condition. - Main thread then calls pthread_cond_broadcast() without holding mutex, - which calls: - - futex(uaddr1, FUTEX_CMP_REQUEUE_PRIVATE, 1, 2147483647, uaddr2, ..) - - This immediately wakes up single thread A, which unlocks mutex and - tries to wake up another thread: - - futex(uaddr2, FUTEX_WAKE_PRIVATE, 1) - - If thread A manages to call futex_wake() before any waiters are - requeued for uaddr2, no other thread is woken up" - -The ordering constraints for the hash bucket waiter counting are that -the waiter counts have to be incremented _before_ getting the spinlock -(because the spinlock acts as part of the memory barrier), but the -"requeue" operation didn't honor those rules, and nobody had even -thought about that case. - -This fairly simple patch just increments the waiter count for the target -hash bucket (hb2) when requeing a futex before taking the locks. It -then decrements them again after releasing the lock - the code that -actually moves the futex(es) between hash buckets will do the additional -required waiter count housekeeping. - -Reported-and-tested-by: Jan Stancek <jstancek@redhat.com> -Acked-by: Davidlohr Bueso <davidlohr@hp.com> -Cc: Peter Zijlstra <peterz@infradead.org> -Cc: Thomas Gleixner <tglx@linutronix.de> -Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> -Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> ---- - kernel/futex.c | 5 +++++ - 1 file changed, 5 insertions(+) - -diff --git a/kernel/futex.c b/kernel/futex.c -index 08ec814..16b1f2c 100644 ---- a/kernel/futex.c -+++ b/kernel/futex.c -@@ -1450,6 +1450,7 @@ retry: - hb2 = hash_futex(&key2); - - retry_private: -+ hb_waiters_inc(hb2); - double_lock_hb(hb1, hb2); - - if (likely(cmpval != NULL)) { -@@ -1459,6 +1460,7 @@ retry_private: - - if (unlikely(ret)) { - double_unlock_hb(hb1, hb2); -+ hb_waiters_dec(hb2); - - ret = get_user(curval, uaddr1); - if (ret) -@@ -1508,6 +1510,7 @@ retry_private: - break; - case -EFAULT: - double_unlock_hb(hb1, hb2); -+ hb_waiters_dec(hb2); - put_futex_key(&key2); - put_futex_key(&key1); - ret = fault_in_user_writeable(uaddr2); -@@ -1517,6 +1520,7 @@ retry_private: - case -EAGAIN: - /* The owner was exiting, try again. */ - double_unlock_hb(hb1, hb2); -+ hb_waiters_dec(hb2); - put_futex_key(&key2); - put_futex_key(&key1); - cond_resched(); -@@ -1592,6 +1596,7 @@ retry_private: - - out_unlock: - double_unlock_hb(hb1, hb2); -+ hb_waiters_dec(hb2); - - /* - * drop_futex_key_refs() must be called outside the spinlocks. During --- -1.9.2 - |