On Wed, Mar 17, 2021 at 07:21:46PM +0800, Qu Wenruo wrote:
>
>
> On 2021/3/17 上午3:43, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@xxxxxx>
> >
> > Commit 1dae796aabf6 ("btrfs: inode: sink parameter start and len to
> > check_data_csum()") replaced the start parameter to check_data_csum()
> > with page_offset(), but page_offset() is not meaningful for direct I/O
> > pages. Bring back the start parameter.
>
> So direct IO pages doesn't have page::index set at all?
No, they don't. Usually you do direct I/O into an anonymous page, but I
suppose you could even do direct I/O into a page mmap'd from another
file or filesystem. In either case, the index isn't meaningful for the
file you're doing direct I/O from.
> Any reproducer? I'd like to try to reproduce it first.
The easiest way to see this issue is to apply this patch:
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2a92211439e8..a962b3026573 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3114,6 +3114,9 @@ static int check_data_csum(struct inode *inode, struct btrfs_io_bio *io_bio,
u8 *csum_expected;
u8 csum[BTRFS_CSUM_SIZE];
+ WARN_ONCE(page_offset(page) + pgoff != start,
+ "page offset %llu != start %llu\n",
+ page_offset(page) + pgoff, start);
ASSERT(pgoff + len <= PAGE_SIZE);
offset_sectors = bio_offset >> fs_info->sectorsize_bits;
Run this simple test:
$ dd if=/dev/zero of=foo bs=4k count=1024
1024+0 records in
1024+0 records out
4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.00456495 s, 919 MB/s
$ sync
$ dd if=foo of=/dev/null iflag=direct bs=4k
1024+0 records in
1024+0 records out
4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.163079 s, 25.7 MB/s
And you'll get a warning like:
[ 84.896486] ------------[ cut here ]------------
[ 84.897370] page offset 94199157981184 != start 0
[ 84.898128] WARNING: CPU: 1 PID: 459 at fs/btrfs/inode.c:3119 check_data_csum+0x189/0x260 [btrfs]
[ 84.899547] Modules linked in: btrfs blake2b_generic xor pata_acpi ata_piix libata scsi_mod raid6_pq virtio_net net_failover virtio_rng libcrc32c rng_core failover
[ 84.901742] CPU: 1 PID: 459 Comm: kworker/u56:2 Not tainted 5.12.0-rc3-00060-ge0cd3910d8cb-dirty #139
[ 84.903205] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 84.904875] Workqueue: btrfs-endio btrfs_work_helper [btrfs]
[ 84.905749] RIP: 0010:check_data_csum+0x189/0x260 [btrfs]
[ 84.906576] Code: 57 11 00 00 0f 85 03 ff ff ff 4c 89 ca 48 c7 c7 50 ba 35 c0 4c 89 44 24 10 48 89 44 24 08 c6 05 04 57 11 00 01 e8 22 e0 cf d4 <0f> 0b 4c 8b 44 24 10 48 8b 44 24 08 e9 d2 fe ff ff 41 8b 45 00 4d
[ 84.909288] RSP: 0018:ffffb6e9c164bb98 EFLAGS: 00010282
[ 84.910061] RAX: 0000000000000000 RBX: ffffe96b84a05f40 RCX: 0000000000000001
[ 84.911109] RDX: 0000000080000001 RSI: ffffffff9573d067 RDI: 00000000ffffffff
[ 84.912149] RBP: 0000000000000000 R08: 0000000000000000 R09: c0000000ffffdfff
[ 84.913197] R10: 0000000000000001 R11: ffffb6e9c164b9c0 R12: 0000000000000000
[ 84.914247] R13: ffff9d32a28c8dc0 R14: ffff9d32ac495e10 R15: 0000000000000004
[ 84.915304] FS: 0000000000000000(0000) GS:ffff9d399f640000(0000) knlGS:0000000000000000
[ 84.916478] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 84.917340] CR2: 000055ad52f97120 CR3: 00000001292f4002 CR4: 0000000000370ee0
[ 84.918435] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 84.919473] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 84.920515] Call Trace:
[ 84.920884] ? find_busiest_group+0x41/0x380
[ 84.921518] ? load_balance+0x176/0xc10
[ 84.922082] ? kvm_sched_clock_read+0x5/0x10
[ 84.922711] ? sched_clock+0x5/0x10
[ 84.923236] btrfs_end_dio_bio+0x2fb/0x310 [btrfs]
[ 84.923982] end_workqueue_fn+0x29/0x40 [btrfs]
[ 84.924698] btrfs_work_helper+0xc1/0x350 [btrfs]
[ 84.925435] process_one_work+0x1c8/0x390
[ 84.926025] ? process_one_work+0x390/0x390
[ 84.926650] worker_thread+0x30/0x370
[ 84.927209] ? process_one_work+0x390/0x390
[ 84.927875] kthread+0x13d/0x160
[ 84.928466] ? kthread_park+0x80/0x80
[ 84.929008] ret_from_fork+0x22/0x30
[ 84.929543] ---[ end trace 4f87c4a13fa476d4 ]---
> >
> > Fixes: 265d4ac03fdf ("btrfs: sink parameter start and len to check_data_csum")
> > Signed-off-by: Omar Sandoval <osandov@xxxxxx>
> > ---
> > fs/btrfs/inode.c | 14 +++++++++-----
> > 1 file changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index ef6cb7b620d0..d2ece8554416 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -2947,11 +2947,13 @@ void btrfs_writepage_endio_finish_ordered(struct page *page, u64 start,
> > * @bio_offset: offset to the beginning of the bio (in bytes)
> > * @page: page where is the data to be verified
> > * @pgoff: offset inside the page
> > + * @start: logical offset in the file
>
> Please add some comment if only for direct IO we need that @start parameter.
Won't that add more confusion? Someone might read that and assume that
they don't need to pass start for a page cache page. In my opinion,
having this change in the git log is enough.
