* Jan Kara jack@suse.cz:
Eric has noticed that after pagecache read rework, generic/418 is occasionally failing for ext4 when blocksize < pagesize. In fact, the pagecache rework just made hard to hit race in ext4 more likely. The problem is that since ext4 conversion of direct IO writes to iomap framework (commit 378f32bab371), we update inode size after direct IO write only after invalidating page cache. Thus if buffered read sneaks at unfortunate moment like:
CPU1 - write at offset 1k CPU2 - read from offset 0 iomap_dio_rw(..., IOMAP_DIO_FORCE_WAIT); ext4_readpage(); ext4_handle_inode_extension()
the read will zero out tail of the page as it still sees smaller inode size and thus page cache becomes inconsistent with on-disk contents with all the consequences.
Fix the problem by moving inode size update into end_io handler which gets called before the page cache is invalidated.
Reported-by: Eric Whitney enwlinux@gmail.com Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure") CC: stable@vger.kernel.org Signed-off-by: Jan Kara jack@suse.cz
fs/ext4/file.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-)
Eric, can you please try whether this patch fixes the failures you are occasionally seeing?
I applied this patch to 5.12-rc7 and ran tests on two different sets of hardware using kvm-xfstests.
5000 runs of generic/418 passed on the 1k test configuration without incident. On an unmodified -rc7 kernel, I'm typically getting 100-200 failures for that many runs. So, that looks good.
After running through all the appliance's test configurations with the patched kernel, I did see one unexpected failure of generic/068 on data=journal due to a burst of kernel warnings. Unexpected means I haven't seen this failure in recent memory on upstream -rc* regression runs. A 10 run attempt to reproduce the failure failed to do so. An instance of the warning follows.
Thanks, Eric
[35456.178585] WARNING: CPU: 1 PID: 22225 at fs/ext4/ext4_jbd2.c:75 ext4_journal_check_start+0x4c/0x90 [35456.180802] Modules linked in: [35456.181554] CPU: 1 PID: 22225 Comm: kworker/u4:0 Not tainted 5.12.0-rc7+ #2 [35456.183169] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 [35456.185030] Workqueue: writeback wb_workfn (flush-254:32) [35456.186290] RIP: 0010:ext4_journal_check_start+0x4c/0x90 [35456.187540] Code: e1 02 75 24 f6 43 50 01 75 54 83 bb 20 03 00 00 04 74 17 48 8b 92 70 03 00 00 31 c0 48 85 d2 74 07 8b 02 83 e0 02 75 06 5b c3 <0f> 0b eb e5 44 8b 42 08 68 11 23 0f 82 48 89 df 45 31 c9 b9 01 00 [35456.190939] RSP: 0018:ffffc90004167850 EFLAGS: 00010246 [35456.191845] RAX: 00000000fffffffb RBX: ffff888009f76000 RCX: 0000000000000000 [35456.193668] RDX: ffff888009f73000 RSI: ffffffff8235dd60 RDI: ffff888009f76000 [35456.195461] RBP: 0000000000000009 R08: 0000000000000000 R09: ffffffff813c9fd8 [35456.197365] R10: 0000000000000000 R11: 000000000002f6b8 R12: 0000000000000000 [35456.199276] R13: 0000000000000008 R14: 0000000000000002 R15: 0000000000000771 [35456.201080] FS: 0000000000000000(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000 [35456.202513] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [35456.203521] CR2: 00007f30cf413000 CR3: 0000000001c04006 CR4: 0000000000370ee0 [35456.205554] Call Trace: [35456.206275] __ext4_journal_start_sb+0x118/0x180 [35456.207568] ext4_writepage+0x368/0x740 [35456.209077] ? _raw_spin_unlock_irqrestore+0x30/0x40 [35456.210638] ? page_mkclean+0x6e/0xc0 [35456.211899] ? lock_is_held_type+0x99/0x100 [35456.213341] __writepage+0x19/0x70 [35456.214614] write_cache_pages+0x1a6/0x470 [35456.216026] ? __wb_calc_thresh+0xd0/0xd0 [35456.217617] generic_writepages+0x59/0x90 [35456.219119] ? lock_is_held_type+0x99/0x100 [35456.220673] ? do_writepages+0x41/0xd0 [35456.222038] ? do_writepages+0x41/0xd0 [35456.223341] ext4_writepages+0xc40/0x1080 [35456.224750] ? __lock_acquire+0x3d5/0x2380 [35456.226175] ? __lock_acquire+0x3d5/0x2380 [35456.227586] ? do_writepages+0x41/0xd0 [35456.228563] ? __ext4_mark_inode_dirty+0x280/0x280 [35456.230308] do_writepages+0x41/0xd0 [35456.231540] ? lock_is_held_type+0x99/0x100 [35456.233032] __writeback_single_inode+0x58/0x530 [35456.234542] writeback_sb_inodes+0x204/0x4d0 [35456.235995] wb_writeback+0x107/0x430 [35456.237489] wb_workfn+0xb5/0x5f0 [35456.238645] ? lock_acquire+0xb5/0x380 [35456.240026] ? process_one_work+0x223/0x5d0 [35456.241522] ? lock_is_held_type+0x99/0x100 [35456.243139] process_one_work+0x2a5/0x5d0 [35456.244615] ? process_one_work+0x5d0/0x5d0 [35456.246108] worker_thread+0x2d/0x3c0 [35456.247429] ? process_one_work+0x5d0/0x5d0 [35456.248926] kthread+0x127/0x140 [35456.250090] ? kthread_park+0x80/0x80 [35456.251379] ret_from_fork+0x22/0x30 [35456.252559] irq event stamp: 4858465 [35456.253785] hardirqs last enabled at (4858473): [<ffffffff8115ddee>] console_unlock+0x36e/0x550 [35456.256235] hardirqs last disabled at (4858482): [<ffffffff8115de77>] console_unlock+0x3f7/0x550 [35456.259117] softirqs last enabled at (4858496): [<ffffffff81c00303>] __do_softirq+0x303/0x41a [35456.261485] softirqs last disabled at (4858491): [<ffffffff810ecade>] irq_exit_rcu+0xae/0xb0 [35456.263742] ---[ end trace ea82423dcfaf8730 ]---
Changes since v1:
- Rewritten the fix to avoid the need for separate transaction handle for orphan list update
diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 194f5d00fa32..be1e80af61be 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -371,15 +371,27 @@ static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset, static int ext4_dio_write_end_io(struct kiocb *iocb, ssize_t size, int error, unsigned int flags) {
- loff_t offset = iocb->ki_pos;
- loff_t pos = iocb->ki_pos; struct inode *inode = file_inode(iocb->ki_filp);
if (error) return error;
- if (size && flags & IOMAP_DIO_UNWRITTEN)
return ext4_convert_unwritten_extents(NULL, inode,offset, size);
- if (size && flags & IOMAP_DIO_UNWRITTEN) {
error = ext4_convert_unwritten_extents(NULL, inode, pos, size);if (error < 0)return error;- }
- /*
* If we are extending the file, we have to update i_size here before* page cache gets invalidated in iomap_dio_rw(). Otherwise racing* buffered reads could zero out too much from page cache pages. Update* of on-disk size will happen later in ext4_dio_write_iter() where* we have enough information to also perform orphan list handling etc.*/- pos += size;
- if (pos > i_size_read(inode))
i_size_write(inode, pos);return 0; } -- 2.26.2