Messages in this thread | | | Subject | Re: [PATCH v2 block/for-linus] writeback: flush inode cgroup wb switches instead of pinning super_block | From | Jens Axboe <> | Date | Tue, 1 Mar 2016 10:46:58 -0700 |
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On 02/29/2016 04:28 PM, Tejun Heo wrote: > If cgroup writeback is in use, inodes can be scheduled for > asynchronous wb switching. Before 5ff8eaac1636 ("writeback: keep > superblock pinned during cgroup writeback association switches"), this > could race with umount leading to super_block being destroyed while > inodes are pinned for wb switching. 5ff8eaac1636 fixed it by bumping > s_active while wb switches are in flight; however, this allowed > in-flight wb switches to make umounts asynchronous when the userland > expected synchronosity - e.g. fsck immediately following umount may > fail because the device is still busy. > > This patch removes the problematic super_block pinning and instead > makes generic_shutdown_super() flush in-flight wb switches. wb > switches are now executed on a dedicated isw_wq so that they can be > flushed and isw_nr_in_flight keeps track of the number of in-flight wb > switches so that flushing can be avoided in most cases. > > v2: Move cgroup_writeback_umount() further below and add MS_ACTIVE > check in inode_switch_wbs() as Jan an Al suggested.
I queued this up for 4.5, but I'm feeling a bit uneasy about it. But it's either that, or revert 5ff8eaac1636 and fix it for real in 4.6. Jan/Tejun, what do you think?
-- Jens Axboe
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