Messages in this thread |  | | Date | Sun, 9 May 2021 11:58:15 +0200 | From | Greg KH <> | Subject | Re: Patch "btrfs: fix a potential hole punching failure" has been added to the 5.4-stable tree |
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On Sat, May 08, 2021 at 12:10:13PM -0400, Sasha Levin wrote: > This is a note to let you know that I've just added the patch titled > > btrfs: fix a potential hole punching failure > > to the 5.4-stable tree which can be found at: > http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary > > The filename of the patch is: > btrfs-fix-a-potential-hole-punching-failure.patch > and it can be found in the queue-5.4 subdirectory. > > If you, or anyone else, feels it should not be added to the stable tree, > please let <stable@vger.kernel.org> know about it. > > > > commit 3744bdfd37eaa635ddb70f15fe5d3bde233e54f0 > Author: BingJing Chang <bingjingc@synology.com> > Date: Thu Mar 25 09:56:22 2021 +0800 > > btrfs: fix a potential hole punching failure > > [ Upstream commit 3227788cd369d734d2d3cd94f8af7536b60fa552 ] > > In commit d77815461f04 ("btrfs: Avoid trucating page or punching hole > in a already existed hole."), existing holes can be skipped by calling > find_first_non_hole() to adjust start and len. However, if the given len > is invalid and large, when an EXTENT_MAP_HOLE extent is found, len will > not be set to zero because (em->start + em->len) is less than > (start + len). Then the ret will be 1 but len will not be set to 0. > The propagated non-zero ret will result in fallocate failure. > > In the while-loop of btrfs_replace_file_extents(), len is not updated > every time before it calls find_first_non_hole(). That is, after > btrfs_drop_extents() successfully drops the last non-hole file extent, > it may fail with ENOSPC when attempting to drop a file extent item > representing a hole. The problem can happen. After it calls > find_first_non_hole(), the cur_offset will be adjusted to be larger > than or equal to end. However, since the len is not set to zero, the > break-loop condition (ret && !len) will not be met. After it leaves the > while-loop, fallocate will return 1, which is an unexpected return > value. > > We're not able to construct a reproducible way to let > btrfs_drop_extents() fail with ENOSPC after it drops the last non-hole > file extent but with remaining holes left. However, it's quite easy to > fix. We just need to update and check the len every time before we call > find_first_non_hole(). To make the while loop more readable, we also > pull the variable updates to the bottom of loop like this: > while (cur_offset < end) { > ... > // update cur_offset & len > // advance cur_offset & len in hole-punching case if needed > } > > Reported-by: Robbie Ko <robbieko@synology.com> > Fixes: d77815461f04 ("btrfs: Avoid trucating page or punching hole in a already existed hole.") > CC: stable@vger.kernel.org # 4.4+ > Reviewed-by: Robbie Ko <robbieko@synology.com> > Reviewed-by: Chung-Chiang Cheng <cccheng@synology.com> > Reviewed-by: Filipe Manana <fdmanana@suse.com> > Signed-off-by: BingJing Chang <bingjingc@synology.com> > Signed-off-by: David Sterba <dsterba@suse.com> > Signed-off-by: Sasha Levin <sashal@kernel.org> > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > index f8e5c47b95e4..dc6f4bfd9a45 100644 > --- a/fs/btrfs/file.c > +++ b/fs/btrfs/file.c > @@ -2642,8 +2642,6 @@ int btrfs_punch_hole_range(struct inode *inode, struct btrfs_path *path, > clone_info->file_offset += clone_len; > } > > - cur_offset = drop_end; > - > ret = btrfs_update_inode(trans, root, inode); > if (ret) > break; > @@ -2663,7 +2661,9 @@ int btrfs_punch_hole_range(struct inode *inode, struct btrfs_path *path, > BUG_ON(ret); /* shouldn't happen */ > trans->block_rsv = rsv; > > - if (!clone_info) { > + cur_offset = drop_args.drop_end; > + len = end - cur_offset; > + if (!clone_info && len) { > ret = find_first_non_hole(inode, &cur_offset, &len); > if (unlikely(ret < 0)) > break;
This broke the build, so I'm dropping it :(
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