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author | Filipe Manana <fdmanana@suse.com> | 2014-07-31 13:41:07 (GMT) |
---|---|---|
committer | Chris Mason <clm@fb.com> | 2014-08-21 14:55:21 (GMT) |
commit | 9c3b306e1c9e6be4be09e99a8fe2227d1005effc (patch) | |
tree | 3959abb99f9d14ae1ab26c0c2735e56504e5939b /fs/btrfs/ioctl.c | |
parent | 87fa3bb0786f37dff0b92f2c38421dd56d8902a9 (diff) | |
download | linux-9c3b306e1c9e6be4be09e99a8fe2227d1005effc.tar.xz |
Btrfs: race free update of commit root for ro snapshots
This is a better solution for the problem addressed in the following
commit:
Btrfs: update commit root on snapshot creation after orphan cleanup
(3821f348889e506efbd268cc8149e0ebfa47c4e5)
The previous solution wasn't the best because of 2 reasons:
1) It added another full transaction commit, which is more expensive
than just swapping the commit root with the root;
2) If a reboot happened after the first transaction commit (the one
that creates the snapshot) and before the second transaction commit,
then we would end up with the same problem if a send using that
snapshot was requested before the first transaction commit after
the reboot.
This change addresses those 2 issues. The second issue is addressed by
switching the commit root in the dentry lookup VFS callback, which is
also called by the snapshot/subvol creation ioctl and performs orphan
cleanup if needed. Like the vfs, the ioctl locks the parent inode too,
preventing race issues between a dentry lookup and snapshot creation.
Cc: Alex Lyakas <alex.btrfs@zadarastorage.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs/btrfs/ioctl.c')
-rw-r--r-- | fs/btrfs/ioctl.c | 33 |
1 files changed, 0 insertions, 33 deletions
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 47aceb4..845287c 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -711,39 +711,6 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir, if (ret) goto fail; - ret = btrfs_orphan_cleanup(pending_snapshot->snap); - if (ret) - goto fail; - - /* - * If orphan cleanup did remove any orphans, it means the tree was - * modified and therefore the commit root is not the same as the - * current root anymore. This is a problem, because send uses the - * commit root and therefore can see inode items that don't exist - * in the current root anymore, and for example make calls to - * btrfs_iget, which will do tree lookups based on the current root - * and not on the commit root. Those lookups will fail, returning a - * -ESTALE error, and making send fail with that error. So make sure - * a send does not see any orphans we have just removed, and that it - * will see the same inodes regardless of whether a transaction - * commit happened before it started (meaning that the commit root - * will be the same as the current root) or not. - */ - if (readonly && pending_snapshot->snap->node != - pending_snapshot->snap->commit_root) { - trans = btrfs_join_transaction(pending_snapshot->snap); - if (IS_ERR(trans) && PTR_ERR(trans) != -ENOENT) { - ret = PTR_ERR(trans); - goto fail; - } - if (!IS_ERR(trans)) { - ret = btrfs_commit_transaction(trans, - pending_snapshot->snap); - if (ret) - goto fail; - } - } - inode = btrfs_lookup_dentry(dentry->d_parent->d_inode, dentry); if (IS_ERR(inode)) { ret = PTR_ERR(inode); |