Messages in this thread | | | Date | Mon, 29 Feb 2016 20:54:28 +0000 | From | Al Viro <> | Subject | Re: [PATCH block/for-linus] writeback: flush inode cgroup wb switches instead of pinning super_block |
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On Mon, Feb 29, 2016 at 03:47:24PM -0500, 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.
Wait a bloody minute. What's to prevent shrink_dcache_for_umount() from dirtying more inodes, triggering more of the same?
> - if (!atomic_inc_not_zero(&inode->i_sb->s_active)) > - goto out_unlock;
This would've failed for inodes on superblock in the middle of shutdown; what's to do the same for the new variant?
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