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author | Lai Jiangshan <laijs@cn.fujitsu.com> | 2013-07-24 12:31:42 +0200 |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2013-07-24 18:24:25 +0200 |
commit | c2fda509667b0fda4372a237f5a59ea4570b1627 (patch) | |
tree | 27ba4e2f32cdd58e2f6f2cfa694f25afe7020e35 | |
parent | Linux 3.11-rc1 (diff) | |
download | linux-c2fda509667b0fda4372a237f5a59ea4570b1627.tar.xz linux-c2fda509667b0fda4372a237f5a59ea4570b1627.zip |
workqueue: allow work_on_cpu() to be called recursively
If the @fn call work_on_cpu() again, the lockdep will complain:
> [ INFO: possible recursive locking detected ]
> 3.11.0-rc1-lockdep-fix-a #6 Not tainted
> ---------------------------------------------
> kworker/0:1/142 is trying to acquire lock:
> ((&wfc.work)){+.+.+.}, at: [<ffffffff81077100>] flush_work+0x0/0xb0
>
> but task is already holding lock:
> ((&wfc.work)){+.+.+.}, at: [<ffffffff81075dd9>] process_one_work+0x169/0x610
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock((&wfc.work));
> lock((&wfc.work));
>
> *** DEADLOCK ***
It is false-positive lockdep report. In this sutiation,
the two "wfc"s of the two work_on_cpu() are different,
they are both on stack. flush_work() can't be deadlock.
To fix this, we need to avoid the lockdep checking in this case,
thus we instroduce a internal __flush_work() which skip the lockdep.
tj: Minor comment adjustment.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reported-by: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Reported-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
-rw-r--r-- | kernel/workqueue.c | 32 |
1 files changed, 22 insertions, 10 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index f02c4a4a0c3c..55f5f0afcd0d 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2817,6 +2817,19 @@ already_gone: return false; } +static bool __flush_work(struct work_struct *work) +{ + struct wq_barrier barr; + + if (start_flush_work(work, &barr)) { + wait_for_completion(&barr.done); + destroy_work_on_stack(&barr.work); + return true; + } else { + return false; + } +} + /** * flush_work - wait for a work to finish executing the last queueing instance * @work: the work to flush @@ -2830,18 +2843,10 @@ already_gone: */ bool flush_work(struct work_struct *work) { - struct wq_barrier barr; - lock_map_acquire(&work->lockdep_map); lock_map_release(&work->lockdep_map); - if (start_flush_work(work, &barr)) { - wait_for_completion(&barr.done); - destroy_work_on_stack(&barr.work); - return true; - } else { - return false; - } + return __flush_work(work); } EXPORT_SYMBOL_GPL(flush_work); @@ -4756,7 +4761,14 @@ long work_on_cpu(int cpu, long (*fn)(void *), void *arg) INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn); schedule_work_on(cpu, &wfc.work); - flush_work(&wfc.work); + + /* + * The work item is on-stack and can't lead to deadlock through + * flushing. Use __flush_work() to avoid spurious lockdep warnings + * when work_on_cpu()s are nested. + */ + __flush_work(&wfc.work); + return wfc.ret; } EXPORT_SYMBOL_GPL(work_on_cpu); |