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author | Filipe Manana <fdmanana@suse.com> | 2021-07-20 18:03:40 +0300 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-09-18 14:42:15 +0300 |
commit | 7d673ab0250e8334573af9d96a2d5053fcc24f51 (patch) | |
tree | 1bcf579882300f2f5b8364f780030889bdf5416d | |
parent | 6e57056734e02bd31be43bb15ed3311b36d69da7 (diff) | |
download | linux-7d673ab0250e8334573af9d96a2d5053fcc24f51.tar.xz |
btrfs: remove racy and unnecessary inode transaction update when using no-holes
[ Upstream commit cceaa89f02f15f232391ae4be214137b0a0285c0 ]
When using the NO_HOLES feature and expanding the size of an inode, we
update the inode's last_trans, last_sub_trans and last_log_commit fields
at maybe_insert_hole() so that a fsync does know that the inode needs to
be logged (by making sure that btrfs_inode_in_log() returns false). This
happens for expanding truncate operations, buffered writes, direct IO
writes and when cloning extents to an offset greater than the inode's
i_size.
However the way we do it is racy, because in between setting the inode's
last_sub_trans and last_log_commit fields, the log transaction ID that was
assigned to last_sub_trans might be committed before we read the root's
last_log_commit and assign that value to last_log_commit. If that happens
it would make a future call to btrfs_inode_in_log() return true. This is
a race that should be extremely unlikely to be hit in practice, and it is
the same that was described by commit bc0939fcfab0d7 ("btrfs: fix race
between marking inode needs to be logged and log syncing").
The fix would simply be to set last_log_commit to the value we assigned
to last_sub_trans minus 1, like it was done in that commit. However
updating these two fields plus the last_trans field is pointless here
because all the callers of btrfs_cont_expand() (which is the only
caller of maybe_insert_hole()) always call btrfs_set_inode_last_trans()
or btrfs_update_inode() after calling btrfs_cont_expand(). Calling either
btrfs_set_inode_last_trans() or btrfs_update_inode() guarantees that the
next fsync will log the inode, as it makes btrfs_inode_in_log() return
false.
So just remove the code that explicitly sets the inode's last_trans,
last_sub_trans and last_log_commit fields.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
-rw-r--r-- | fs/btrfs/inode.c | 12 |
1 files changed, 5 insertions, 7 deletions
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index c3810c6430d9..044300db5e22 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5064,15 +5064,13 @@ static int maybe_insert_hole(struct btrfs_root *root, struct btrfs_inode *inode, int ret; /* - * Still need to make sure the inode looks like it's been updated so - * that any holes get logged if we fsync. + * If NO_HOLES is enabled, we don't need to do anything. + * Later, up in the call chain, either btrfs_set_inode_last_sub_trans() + * or btrfs_update_inode() will be called, which guarantee that the next + * fsync will know this inode was changed and needs to be logged. */ - if (btrfs_fs_incompat(fs_info, NO_HOLES)) { - inode->last_trans = fs_info->generation; - inode->last_sub_trans = root->log_transid; - inode->last_log_commit = root->last_log_commit; + if (btrfs_fs_incompat(fs_info, NO_HOLES)) return 0; - } /* * 1 - for the one we're dropping |