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authorTejun Heo <tj@kernel.org>2016-03-01 02:28:53 +0300
committerJens Axboe <axboe@fb.com>2016-03-04 00:42:50 +0300
commita1a0e23e49037c23ea84bc8cc146a03584d13577 (patch)
treeb8bb7792ed9dd97358bdea0a6a2f36fdb617bbf0 /include/linux/writeback.h
parente9fc63d682dbbef17921aeb00d03fd52d6735ffd (diff)
downloadlinux-a1a0e23e49037c23ea84bc8cc146a03584d13577.tar.xz
writeback: flush inode cgroup wb switches instead of pinning super_block
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. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Tahsin Erdogan <tahsin@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Al Viro <viro@ZenIV.linux.org.uk> Link: http://lkml.kernel.org/g/CAAeU0aNCq7LGODvVGRU-oU_o-6enii5ey0p1c26D1ZzYwkDc5A@mail.gmail.com Fixes: 5ff8eaac1636 ("writeback: keep superblock pinned during cgroup writeback association switches") Cc: stable@vger.kernel.org #v4.5 Reviewed-by: Jan Kara <jack@suse.cz> Tested-by: Tahsin Erdogan <tahsin@google.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'include/linux/writeback.h')
-rw-r--r--include/linux/writeback.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index b333c945e571..d0b5ca5d4e08 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -198,6 +198,7 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
void wbc_detach_inode(struct writeback_control *wbc);
void wbc_account_io(struct writeback_control *wbc, struct page *page,
size_t bytes);
+void cgroup_writeback_umount(void);
/**
* inode_attach_wb - associate an inode with its wb
@@ -301,6 +302,10 @@ static inline void wbc_account_io(struct writeback_control *wbc,
{
}
+static inline void cgroup_writeback_umount(void)
+{
+}
+
#endif /* CONFIG_CGROUP_WRITEBACK */
/*