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authorDarrick J. Wong <djwong@kernel.org>2021-08-20 14:42:39 -0700
committerDarrick J. Wong <djwong@kernel.org>2021-08-23 17:32:51 -0700
commit72a048c1056a72e37ea2ee34cc73d8c6d6cb4290 (patch)
tree4742b932bdfa9e367c03dff9d40a3d9a3250e3b4 /fs/xfs
parent61e0d0cc51cd6b9d7447923f3ac7e60049de3e2e (diff)
downloadlinux-72a048c1056a72e37ea2ee34cc73d8c6d6cb4290.tar.bz2
xfs: only set IOMAP_F_SHARED when providing a srcmap to a write
While prototyping a free space defragmentation tool, I observed an unexpected IO error while running a sequence of commands that can be recreated by the following sequence of commands: # xfs_io -f -c "pwrite -S 0x58 -b 10m 0 10m" file1 # cp --reflink=always file1 file2 # punch-alternating -o 1 file2 # xfs_io -c "funshare 0 10m" file2 fallocate: Input/output error I then scraped this (abbreviated) stack trace from dmesg: WARNING: CPU: 0 PID: 30788 at fs/iomap/buffered-io.c:577 iomap_write_begin+0x376/0x450 CPU: 0 PID: 30788 Comm: xfs_io Not tainted 5.14.0-rc6-xfsx #rc6 5ef57b62a900814b3e4d885c755e9014541c8732 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014 RIP: 0010:iomap_write_begin+0x376/0x450 RSP: 0018:ffffc90000c0fc20 EFLAGS: 00010297 RAX: 0000000000000001 RBX: ffffc90000c0fd10 RCX: 0000000000001000 RDX: ffffc90000c0fc54 RSI: 000000000000000c RDI: 000000000000000c RBP: ffff888005d5dbd8 R08: 0000000000102000 R09: ffffc90000c0fc50 R10: 0000000000b00000 R11: 0000000000101000 R12: ffffea0000336c40 R13: 0000000000001000 R14: ffffc90000c0fd10 R15: 0000000000101000 FS: 00007f4b8f62fe40(0000) GS:ffff88803ec00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000056361c554108 CR3: 000000000524e004 CR4: 00000000001706f0 Call Trace: iomap_unshare_actor+0x95/0x140 iomap_apply+0xfa/0x300 iomap_file_unshare+0x44/0x60 xfs_reflink_unshare+0x50/0x140 [xfs 61947ea9b3a73e79d747dbc1b90205e7987e4195] xfs_file_fallocate+0x27c/0x610 [xfs 61947ea9b3a73e79d747dbc1b90205e7987e4195] vfs_fallocate+0x133/0x330 __x64_sys_fallocate+0x3e/0x70 do_syscall_64+0x35/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f4b8f79140a Looking at the iomap tracepoints, I saw this: iomap_iter: dev 8:64 ino 0x100 pos 0 length 0 flags WRITE|0x80 (0x81) ops xfs_buffered_write_iomap_ops caller iomap_file_unshare iomap_iter_dstmap: dev 8:64 ino 0x100 bdev 8:64 addr -1 offset 0 length 131072 type DELALLOC flags SHARED iomap_iter_srcmap: dev 8:64 ino 0x100 bdev 8:64 addr 147456 offset 0 length 4096 type MAPPED flags iomap_iter: dev 8:64 ino 0x100 pos 0 length 4096 flags WRITE|0x80 (0x81) ops xfs_buffered_write_iomap_ops caller iomap_file_unshare iomap_iter_dstmap: dev 8:64 ino 0x100 bdev 8:64 addr -1 offset 4096 length 4096 type DELALLOC flags SHARED console: WARNING: CPU: 0 PID: 30788 at fs/iomap/buffered-io.c:577 iomap_write_begin+0x376/0x450 The first time funshare calls ->iomap_begin, xfs sees that the first block is shared and creates a 128k delalloc reservation in the COW fork. The delalloc reservation is returned as dstmap, and the shared block is returned as srcmap. So far so good. funshare calls ->iomap_begin to try the second block. This time there's no srcmap (punch-alternating punched it out!) but we still have the delalloc reservation in the COW fork. Therefore, we again return the reservation as dstmap and the hole as srcmap. iomap_unshare_iter incorrectly tries to unshare the hole, which __iomap_write_begin rejects because shared regions must be fully written and therefore cannot require zeroing. Therefore, change the buffered write iomap_begin function not to set IOMAP_F_SHARED when there isn't a source mapping to read from for the unsharing. Signed-off-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Diffstat (limited to 'fs/xfs')
-rw-r--r--fs/xfs/xfs_iomap.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 7c69b124a475..093758440ad5 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1064,11 +1064,11 @@ found_cow:
error = xfs_bmbt_to_iomap(ip, srcmap, &imap, 0);
if (error)
return error;
- } else {
- xfs_trim_extent(&cmap, offset_fsb,
- imap.br_startoff - offset_fsb);
+ return xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED);
}
- return xfs_bmbt_to_iomap(ip, iomap, &cmap, IOMAP_F_SHARED);
+
+ xfs_trim_extent(&cmap, offset_fsb, imap.br_startoff - offset_fsb);
+ return xfs_bmbt_to_iomap(ip, iomap, &cmap, 0);
out_unlock:
xfs_iunlock(ip, XFS_ILOCK_EXCL);