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bdi: avoid oops on device removal 

After commit 839a8e8660 ("writeback: replace custom worker pool
implementation with unbound workqueue") when device is removed while we
are writing to it we crash in bdi_writeback_workfn() ->
set_worker_desc() because bdi->dev is NULL.

This can happen because even though bdi_unregister() cancels all pending
flushing work, nothing really prevents new ones from being queued from
balance_dirty_pages() or other places.

Fix the problem by clearing BDI_registered bit in bdi_unregister() and
checking it before scheduling of any flushing work.

Fixes: 839a8e8660

Reviewed-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Derek Basehore <dbasehore@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jan Kara 2014-04-03 14:46:23 -07:00 committed by Linus Torvalds
parent 6ca738d60c
commit 5acda9d12d
3 changed files with 28 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
fs/fs-writeback.c
View File

@ -89,16 +89,29 @@ static inline struct inode *wb_inode(struct list_head *head)
#define CREATE_TRACE_POINTS
#include <trace/events/writeback.h>
static void bdi_wakeup_thread(struct backing_dev_info *bdi)
{
spin_lock_bh(&bdi->wb_lock);
if (test_bit(BDI_registered, &bdi->state))
mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
spin_unlock_bh(&bdi->wb_lock);
}
static void bdi_queue_work(struct backing_dev_info *bdi,
struct wb_writeback_work *work)
{
trace_writeback_queue(bdi, work);
spin_lock_bh(&bdi->wb_lock);
if (!test_bit(BDI_registered, &bdi->state)) {
if (work->done)
complete(work->done);
goto out_unlock;
}
list_add_tail(&work->list, &bdi->work_list);
spin_unlock_bh(&bdi->wb_lock);
mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
out_unlock:
spin_unlock_bh(&bdi->wb_lock);
}
static void
@ -114,7 +127,7 @@ __bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages,
work = kzalloc(sizeof(*work), GFP_ATOMIC);
if (!work) {
trace_writeback_nowork(bdi);
mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
bdi_wakeup_thread(bdi);
return;
}
@ -161,7 +174,7 @@ void bdi_start_background_writeback(struct backing_dev_info *bdi)
* writeback as soon as there is no other work to do.
*/
trace_writeback_wake_background(bdi);
mod_delayed_work(bdi_wq, &bdi->wb.dwork, 0);
bdi_wakeup_thread(bdi);
}
/*
@ -1017,7 +1030,7 @@ void bdi_writeback_workfn(struct work_struct *work)
current->flags |= PF_SWAPWRITE;
if (likely(!current_is_workqueue_rescuer() ||
list_empty(&bdi->bdi_list))) {
!test_bit(BDI_registered, &bdi->state))) {
/*
* The normal path. Keep writing back @bdi until its
* work_list is empty. Note that this path is also taken

2
include/linux/backing-dev.h
View File

@ -95,7 +95,7 @@ struct backing_dev_info {
unsigned int max_ratio, max_prop_frac;
struct bdi_writeback wb; /* default writeback info for this bdi */
spinlock_t wb_lock; /* protects work_list */
spinlock_t wb_lock; /* protects work_list & wb.dwork scheduling */
struct list_head work_list;

13
mm/backing-dev.c
View File

@ -297,7 +297,10 @@ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
unsigned long timeout;
timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
spin_lock_bh(&bdi->wb_lock);
if (test_bit(BDI_registered, &bdi->state))
queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout);
spin_unlock_bh(&bdi->wb_lock);
}
/*
@ -310,9 +313,6 @@ static void bdi_remove_from_list(struct backing_dev_info *bdi)
spin_unlock_bh(&bdi_lock);
synchronize_rcu_expedited();
/* bdi_list is now unused, clear it to mark @bdi dying */
INIT_LIST_HEAD(&bdi->bdi_list);
}
int bdi_register(struct backing_dev_info *bdi, struct device *parent,
@ -363,6 +363,11 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
*/
bdi_remove_from_list(bdi);
/* Make sure nobody queues further work */
spin_lock_bh(&bdi->wb_lock);
clear_bit(BDI_registered, &bdi->state);
spin_unlock_bh(&bdi->wb_lock);
/*
* Drain work list and shutdown the delayed_work. At this point,
* @bdi->bdi_list is empty telling bdi_Writeback_workfn() that @bdi