Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=13c22168b7276dffe49dc66675d5a78f6d288e0d
Commit:     13c22168b7276dffe49dc66675d5a78f6d288e0d
Parent:     87a7defb0d4255d5aea2c5067813b26836127983
Author:     Oleg Nesterov <[EMAIL PROTECTED]>
AuthorDate: Tue Jul 17 04:03:55 2007 -0700
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Tue Jul 17 10:23:03 2007 -0700

    destroy_workqueue() can livelock
    
    Pointed out by Michal Schmidt <[EMAIL PROTECTED]>.
    
    The bug was introduced in 2.6.22 by me.
    
    cleanup_workqueue_thread() does flush_cpu_workqueue(cwq) in a loop until
    ->worklist becomes empty.  This is live-lockable, a re-niced caller can get
    CPU after wake_up() and insert a new barrier before the lower-priority
    cwq->thread has a chance to clear ->current_work.
    
    Change cleanup_workqueue_thread() to do flush_cpu_workqueue(cwq) only once.
     We can rely on the fact that run_workqueue() won't return until it flushes
    all works.  So it is safe to call kthread_stop() after that, the "should
    stop" request won't be noticed until run_workqueue() returns.
    
    Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>
    Cc: Michal Schmidt <[EMAIL PROTECTED]>
    Cc: Srivatsa Vaddagiri <[EMAIL PROTECTED]>
    Cc: <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 kernel/workqueue.c |   11 +++++------
 1 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1935302..58e5c15 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -752,18 +752,17 @@ static void cleanup_workqueue_thread(struct 
cpu_workqueue_struct *cwq, int cpu)
        if (cwq->thread == NULL)
                return;
 
+       flush_cpu_workqueue(cwq);
        /*
-        * If the caller is CPU_DEAD the single flush_cpu_workqueue()
-        * is not enough, a concurrent flush_workqueue() can insert a
-        * barrier after us.
+        * If the caller is CPU_DEAD and cwq->worklist was not empty,
+        * a concurrent flush_workqueue() can insert a barrier after us.
+        * However, in that case run_workqueue() won't return and check
+        * kthread_should_stop() until it flushes all work_struct's.
         * When ->worklist becomes empty it is safe to exit because no
         * more work_structs can be queued on this cwq: flush_workqueue
         * checks list_empty(), and a "normal" queue_work() can't use
         * a dead CPU.
         */
-       while (flush_cpu_workqueue(cwq))
-               ;
-
        kthread_stop(cwq->thread);
        cwq->thread = NULL;
 }
-
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