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| author | Artem Bityutskiy <Artem.Bityutskiy@nokia.com> | 2010-07-25 13:29:13 +0200 |
|---|---|---|
| committer | Jens Axboe <jaxboe@fusionio.com> | 2010-08-07 18:53:55 +0200 |
| commit | c5f7ad233b8805dae06e694538d8095b19f3c560 (patch) | |
| tree | c47a1991fe1de055cfd06f5cecb8cfaa9f497ed7 | |
| parent | writeback: fix possible race when creating bdi threads (diff) | |
| download | linux-c5f7ad233b8805dae06e694538d8095b19f3c560.tar.xz linux-c5f7ad233b8805dae06e694538d8095b19f3c560.zip | |
writeback: do not lose wake-ups in the forker thread - 1
Currently the forker thread can lose wake-ups which may lead to unnecessary
delays in processing bdi works. E.g., consider the following scenario.
1. 'bdi_forker_thread()' walks the 'bdi_list', finds out there is nothing to
do, and is about to finish the loop.
2. A bdi thread decides to exit because it was inactive for long time.
3. 'bdi_queue_work()' adds a work to the bdi which just exited, so it wakes up
the forker thread.
4. but 'bdi_forker_thread()' executes 'set_current_state(TASK_INTERRUPTIBLE)'
and goes sleep. We lose a wake-up.
Losing the wake-up is not fatal, but this means that the bdi work processing
will be delayed by up to 5 sec. This race is theoretical, I never hit it, but
it is worth fixing.
The fix is to execute 'set_current_state(TASK_INTERRUPTIBLE)' _before_ walking
'bdi_list', not after.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
| -rw-r--r-- | mm/backing-dev.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 327e36d1d623..b1dc2d4b9cdd 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -342,6 +342,7 @@ static int bdi_forker_thread(void *ptr) wb_do_writeback(me, 0); spin_lock_bh(&bdi_lock); + set_current_state(TASK_INTERRUPTIBLE); /* * Check if any existing bdi's have dirty data without @@ -357,8 +358,6 @@ static int bdi_forker_thread(void *ptr) bdi_add_default_flusher_thread(bdi); } - set_current_state(TASK_INTERRUPTIBLE); - if (list_empty(&bdi_pending_list)) { unsigned long wait; |