From 8a32c441c1609f80e55df75422324a1151208f40 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:23 -0800 Subject: freezer: implement and use kthread_freezable_should_stop() Writeback and thinkpad_acpi have been using thaw_process() to prevent deadlock between the freezer and kthread_stop(); unfortunately, this is inherently racy - nothing prevents freezing from happening between thaw_process() and kthread_stop(). This patch implements kthread_freezable_should_stop() which enters refrigerator if necessary but is guaranteed to return if kthread_stop() is invoked. Both thaw_process() users are converted to use the new function. Note that this deadlock condition exists for many of freezable kthreads. They need to be converted to use the new should_stop or freezable workqueue. Tested with synthetic test case. Signed-off-by: Tejun Heo Acked-by: Henrique de Moraes Holschuh Cc: Jens Axboe Cc: Oleg Nesterov --- mm/backing-dev.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) (limited to 'mm') diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 71034f41a2ba..7ba8feae11b8 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -600,14 +600,10 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi) /* * Finally, kill the kernel thread. We don't need to be RCU - * safe anymore, since the bdi is gone from visibility. Force - * unfreeze of the thread before calling kthread_stop(), otherwise - * it would never exet if it is currently stuck in the refrigerator. + * safe anymore, since the bdi is gone from visibility. */ - if (bdi->wb.task) { - thaw_process(bdi->wb.task); + if (bdi->wb.task) kthread_stop(bdi->wb.task); - } } /* -- cgit v1.2.3 From a5be2d0d1a8746e7be5210e3d6b904455000443c Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 21 Nov 2011 12:32:23 -0800 Subject: freezer: rename thaw_process() to __thaw_task() and simplify the implementation thaw_process() now has only internal users - system and cgroup freezers. Remove the unnecessary return value, rename, unexport and collapse __thaw_process() into it. This will help further updates to the freezer code. -v3: oom_kill grew a use of thaw_process() while this patch was pending. Convert it to use __thaw_task() for now. In the longer term, this should be handled by allowing tasks to die if killed even if it's frozen. -v2: minor style update as suggested by Matt. Signed-off-by: Tejun Heo Cc: Paul Menage Cc: Matt Helsley --- mm/oom_kill.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm') diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 76f2c5ae908e..3134ee2fb2e8 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -328,7 +328,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints, */ if (test_tsk_thread_flag(p, TIF_MEMDIE)) { if (unlikely(frozen(p))) - thaw_process(p); + __thaw_task(p); return ERR_PTR(-1UL); } if (!p->mm) -- cgit v1.2.3