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author | Artem Bityutskiy <Artem.Bityutskiy@nokia.com> | 2010-07-25 13:29:12 +0200 |
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committer | Jens Axboe <jaxboe@fusionio.com> | 2010-08-07 18:53:19 +0200 |
commit | 94eac5e62364df4e605e451218ee6024a7ba664f (patch) | |
tree | 5e4b7d85361ad20821ba3371acc1536262846f22 /mm | |
parent | writeback: harmonize writeback threads naming (diff) | |
download | linux-94eac5e62364df4e605e451218ee6024a7ba664f.tar.xz linux-94eac5e62364df4e605e451218ee6024a7ba664f.zip |
writeback: fix possible race when creating bdi threads
This patch fixes a very unlikely race condition on the bdi forker thread error
path: when bdi thread creation fails, 'bdi->wb.task' may contain the error code
for a short period of time. If at the same time someone submits a work to this
bdi, we can end up with an oops 'bdi_queue_work()' while executing
'wake_up_process(wb->task)'.
This patch fixes the issue by introducing a temporary variable 'task' and
storing the possible error code there, so that 'wb->task' would never take
erroneous values.
Note, this race is very unlikely and I never hit it, so it is theoretical, but
nevertheless worth fixing.
This patch also merges 2 comments which were previously separate.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/backing-dev.c | 28 |
1 files changed, 11 insertions, 17 deletions
diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 4e9ed2a8521f..327e36d1d623 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -331,8 +331,8 @@ static int bdi_forker_thread(void *ptr) set_user_nice(current, 0); for (;;) { + struct task_struct *task; struct backing_dev_info *bdi, *tmp; - struct bdi_writeback *wb; /* * Temporary measure, we want to make sure we don't see @@ -383,29 +383,23 @@ static int bdi_forker_thread(void *ptr) list_del_init(&bdi->bdi_list); spin_unlock_bh(&bdi_lock); - wb = &bdi->wb; - wb->task = kthread_run(bdi_writeback_thread, wb, "flush-%s", - dev_name(bdi->dev)); - /* - * If thread creation fails, then readd the bdi to - * the pending list and force writeout of the bdi - * from this forker thread. That will free some memory - * and we can try again. - */ - if (IS_ERR(wb->task)) { - wb->task = NULL; - + task = kthread_run(bdi_writeback_thread, &bdi->wb, "flush-%s", + dev_name(bdi->dev)); + if (IS_ERR(task)) { /* - * Add this 'bdi' to the back, so we get - * a chance to flush other bdi's to free - * memory. + * If thread creation fails, then readd the bdi back to + * the list and force writeout of the bdi from this + * forker thread. That will free some memory and we can + * try again. Add it to the tail so we get a chance to + * flush other bdi's to free memory. */ spin_lock_bh(&bdi_lock); list_add_tail(&bdi->bdi_list, &bdi_pending_list); spin_unlock_bh(&bdi_lock); bdi_flush_io(bdi); - } + } else + bdi->wb.task = task; } return 0; |