Messages in this thread |  | | Date | Thu, 19 Dec 2019 18:06:49 -0500 | From | Sasha Levin <> | Subject | Re: [PATCH AUTOSEL 5.4 299/350] btrfs: don't prematurely free work in end_workqueue_fn() |
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On Thu, Dec 12, 2019 at 01:11:03PM +0100, David Sterba wrote: >On Tue, Dec 10, 2019 at 04:06:44PM -0500, Sasha Levin wrote: >> From: Omar Sandoval <osandov@fb.com> >> >> [ Upstream commit 9be490f1e15c34193b1aae17da58e14dd9f55a95 ] >> >> Currently, end_workqueue_fn() frees the end_io_wq entry (which embeds >> the work item) and then calls bio_endio(). This is another potential >> instance of the bug in "btrfs: don't prematurely free work in >> run_ordered_work()". >> >> In particular, the endio call may depend on other work items. For >> example, btrfs_end_dio_bio() can call btrfs_subio_endio_read() -> >> __btrfs_correct_data_nocsum() -> dio_read_error() -> >> submit_dio_repair_bio(), which submits a bio that is also completed >> through a end_workqueue_fn() work item. However, >> __btrfs_correct_data_nocsum() waits for the newly submitted bio to >> complete, thus it depends on another work item. >> >> This example currently usually works because we use different workqueue >> helper functions for BTRFS_WQ_ENDIO_DATA and BTRFS_WQ_ENDIO_DIO_REPAIR. >> However, it may deadlock with stacked filesystems and is fragile >> overall. The proper fix is to free the work item at the very end of the >> work function, so let's do that. >> >> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> >> Signed-off-by: Omar Sandoval <osandov@fb.com> >> Reviewed-by: David Sterba <dsterba@suse.com> >> Signed-off-by: David Sterba <dsterba@suse.com> >> Signed-off-by: Sasha Levin <sashal@kernel.org> > >The were more patches in the series, all contain "don't prematurely free >work in" and were part of a rework of async work processing. They're >fixing a very uncommon usecase, so if there's desire to backport them >the whole series needs to go in. > >In the autosel list, there are only 2 and without the important fix. > >c495dcd6fbe1 btrfs: don't prematurely free work in run_ordered_work() >9be490f1e15c btrfs: don't prematurely free work in end_workqueue_fn() >e732fe95e4ca btrfs: don't prematurely free work in reada_start_machine_worker() >57d4f0b86327 btrfs: don't prematurely free work in scrub_missing_raid56_worker()
I've queued all 4, thanks!
>a0cac0ec961f btrfs: get rid of unique workqueue helper functions >- this is only a cleanup that removes code obsoleted by the fixes above, > probably out of scope of stable > >I have intentionally not tagged the patches for stable, the usecase is >is specific to one user (FB), the known reproducer is only their >workload and the fixes are in their kernel already. > >So if there's desire to add the patches to stable trees, then it has to >be the whole series, but I don't see a strong reason for it.
If it's upstream and broken then it's relevant, it doesn't matter if its one user or a million users.
-- Thanks, Sasha
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