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authorThomas Gleixner <tglx@linutronix.de>2019-11-06 22:55:45 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-12-05 15:38:28 +0100
commite6e00df182908f34360c3c9f2d13cc719362e9c0 (patch)
tree92d3b927fdc9bdcf6f8639d7b65061b153fa0df5 /kernel
parentac7e59a0c1ae35a252b2e9946547b82be90cec36 (diff)
futex: Provide distinct return value when owner is exiting
commit ac31c7ff8624409ba3c4901df9237a616c187a5d upstream. attach_to_pi_owner() returns -EAGAIN for various cases: - Owner task is exiting - Futex value has changed The caller drops the held locks (hash bucket, mmap_sem) and retries the operation. In case of the owner task exiting this can result in a live lock. As a preparatory step for seperating those cases, provide a distinct return value (EBUSY) for the owner exiting case. No functional change. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20191106224556.935606117@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/futex.c16
1 files changed, 9 insertions, 7 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index e6a68380f4de..660d6e259dca 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1182,11 +1182,11 @@ static int handle_exit_race(u32 __user *uaddr, u32 uval,
u32 uval2;
/*
- * If the futex exit state is not yet FUTEX_STATE_DEAD, wait
- * for it to finish.
+ * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
+ * caller that the alleged owner is busy.
*/
if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
- return -EAGAIN;
+ return -EBUSY;
/*
* Reread the user space value to handle the following situation:
@@ -2093,12 +2093,13 @@ retry_private:
if (!ret)
goto retry;
goto out;
+ case -EBUSY:
case -EAGAIN:
/*
* Two reasons for this:
- * - Owner is exiting and we just wait for the
+ * - EBUSY: Owner is exiting and we just wait for the
* exit to complete.
- * - The user space value changed.
+ * - EAGAIN: The user space value changed.
*/
double_unlock_hb(hb1, hb2);
hb_waiters_dec(hb2);
@@ -2859,12 +2860,13 @@ retry_private:
goto out_unlock_put_key;
case -EFAULT:
goto uaddr_faulted;
+ case -EBUSY:
case -EAGAIN:
/*
* Two reasons for this:
- * - Task is exiting and we just wait for the
+ * - EBUSY: Task is exiting and we just wait for the
* exit to complete.
- * - The user space value changed.
+ * - EAGAIN: The user space value changed.
*/
queue_unlock(hb);
put_futex_key(&q.key);