Re: [PATCH 4/7] btrfs: Switch to iomap_dio_rw() for dio

[Filipe Manana <fdmanana@gmail.com>]

On Wed, Jun 3, 2020 at 12:35 PM Filipe Manana <fdmanana@gmail.com> wrote:
>
> On Thu, May 28, 2020 at 7:38 PM Goldwyn Rodrigues <rgoldwyn@suse.de> wrote:
> >
> > On 17:45 28/05, Filipe Manana wrote:
> > > On Thu, May 28, 2020 at 5:34 PM Goldwyn Rodrigues <rgoldwyn@suse.de> wrote:
> > > > > And who locked the extent range before?
> > > >
> > > > This is usually locked by a previous buffered write or read.
> > >
> > > A previous buffered write/read that has already finished or is still
> > > in progress?
> > >
> > > Because if it has finished we're not supposed to have the file range
> > > locked anymore.
> >
> > In progress. Mixing buffered I/O with direct writes.
> >
> > >
> > > >
> > > > >
> > > > > That seems alarming to me, specially if it's a direct IO write failing
> > > > > to invalidate the page cache, since a subsequent buffered read could
> > > > > get stale data (what's in the page cache), and not what the direct IO
> > > > > write wrote.
> > > > >
> > > > > Can you elaborate more on all those details?
> > > >
> > > > The origin of the message is when iomap_dio_rw() tries to invalidate the
> > > > inode pages, but fails and calls dio_warn_stale_pagecache().
> > > >
> > > > In the vanilla code, generic_file_direct_write() aborts direct writes
> > > > and returns 0 so that it may fallback to buffered I/O. Perhaps this
> > > > should be changed in iomap_dio_rw() as well. I will write a patch to
> > > > accomodate that.
> > >
> > > On vanilla we have no problems of mixing buffered and direct
> > > operations as long as they are done sequentially at least.
> > > And even if done concurrently we take several measures to ensure that
> > > are no surprises (locking ranges, waiting for any ordered extents in
> > > progress, etc).
> >
> > Yes, it is because of the code in generic_file_direct_write(). Anyways,
> > I did some tests with the following patch, and it seems to work. I will
> > send a formal patch to so that it gets incorporated in iomap sequence as
> > well.
> >
> > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > index e4addfc58107..215315be6233 100644
> > --- a/fs/iomap/direct-io.c
> > +++ b/fs/iomap/direct-io.c
> > @@ -483,9 +483,15 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> >          */
> >         ret = invalidate_inode_pages2_range(mapping,
> >                         pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
> > -       if (ret)
> > -               dio_warn_stale_pagecache(iocb->ki_filp);
> > -       ret = 0;
> > +       /*
> > +        * If a page can not be invalidated, return 0 to fall back
> > +        * to buffered write.
> > +        */
> > +       if (ret) {
> > +               if (ret == -EBUSY)
> > +                       ret = 0;
> > +               goto out_free_dio;
> > +       }
> >
> >         if (iov_iter_rw(iter) == WRITE && !wait_for_completion &&
> >             !inode->i_sb->s_dio_done_wq) {
> >
> >
>
> Thanks. As I just replied on another thread for that patch, we
> actually have a regression.
> There's more than the annoying warning in dmesg, it also sets -EIO on
> the inode's mapping and makes future fsyncs return that error despite
> the fact that no actual errors or corruptions happened:
>
> https://patchwork.kernel.org/patch/11576677/
>

There's also some deadlock/hang, I have triggered it twice today with
generic/113 on two different VMs:

[14621.297370] INFO: task kworker/1:117:15962 blocked for more than 120 seconds.
[14621.298491]       Not tainted 5.7.0-rc7-btrfs-next-59 #1
[14621.299231] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[14621.300523] kworker/1:117   D    0 15962      2 0x80004000
[14621.301558] Workqueue: dio/sdb iomap_dio_complete_work
[14621.302389] Call Trace:
[14621.302877]  __schedule+0x384/0xa30
[14621.303555]  schedule+0x33/0xe0
[14621.304167]  rwsem_down_write_slowpath+0x2c2/0x750
[14621.305121]  ? btrfs_sync_file+0x1fe/0x4d0 [btrfs]
[14621.306217]  btrfs_sync_file+0x1fe/0x4d0 [btrfs]
[14621.307113]  iomap_dio_complete+0x11b/0x260
[14621.307888]  ? aio_fsync_work+0x5b0/0x5b0
[14621.308585]  iomap_dio_complete_work+0x17/0x30
[14621.309476]  process_one_work+0x275/0x6b0
[14621.310275]  worker_thread+0x4f/0x3e0
[14621.310869]  ? process_one_work+0x6b0/0x6b0
[14621.311403]  kthread+0x12a/0x170
[14621.311819]  ? kthread_create_worker_on_cpu+0x70/0x70
[14621.312460]  ret_from_fork+0x3a/0x50
[14621.312983] INFO: task kworker/1:199:16063 blocked for more than 120 seconds.
[14621.313921]       Not tainted 5.7.0-rc7-btrfs-next-59 #1
[14621.314680] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[14621.315724] kworker/1:199   D    0 16063      2 0x80004000
[14621.316445] Workqueue: dio/sdb iomap_dio_complete_work
[14621.317101] Call Trace:
[14621.317437]  __schedule+0x384/0xa30
[14621.317928]  schedule+0x33/0xe0
[14621.318339]  rwsem_down_write_slowpath+0x2c2/0x750
[14621.318981]  ? btrfs_sync_file+0x1fe/0x4d0 [btrfs]
[14621.319609]  btrfs_sync_file+0x1fe/0x4d0 [btrfs]
[14621.320203]  iomap_dio_complete+0x11b/0x260
[14621.320721]  ? aio_fsync_work+0x5b0/0x5b0
[14621.321249]  iomap_dio_complete_work+0x17/0x30
[14621.321844]  process_one_work+0x275/0x6b0
[14621.322376]  worker_thread+0x4f/0x3e0
[14621.322871]  ? process_one_work+0x6b0/0x6b0
[14621.323408]  kthread+0x12a/0x170
[14621.323827]  ? kthread_create_worker_on_cpu+0x70/0x70
[14621.324473]  ret_from_fork+0x3a/0x50
[14621.324983] INFO: task aio-stress:16274 blocked for more than 120 seconds.
[14621.325896]       Not tainted 5.7.0-rc7-btrfs-next-59 #1
[14621.326579] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[14621.327580] aio-stress      D    0 16274  14855 0x00004000
[14621.328280] Call Trace:
[14621.328602]  __schedule+0x384/0xa30
[14621.329056]  schedule+0x33/0xe0
[14621.329478]  rwsem_down_write_slowpath+0x2c2/0x750
[14621.330118]  ? btrfs_sync_file+0x219/0x4d0 [btrfs]
[14621.330747]  btrfs_sync_file+0x219/0x4d0 [btrfs]
[14621.331346]  iomap_dio_complete+0x11b/0x260
[14621.331886]  iomap_dio_rw+0x3bc/0x4c0
[14621.332372]  ? btrfs_file_write_iter+0x645/0x870 [btrfs]
[14621.333076]  btrfs_file_write_iter+0x645/0x870 [btrfs]
[14621.333749]  aio_write+0x148/0x1d0
[14621.334196]  ? lock_acquire+0xb1/0x4a0
[14621.334682]  ? __might_fault+0x3e/0x90
[14621.335172]  ? __fget_files+0x132/0x270
[14621.335668]  ? io_submit_one+0x946/0x1630
[14621.336184]  io_submit_one+0x946/0x1630
[14621.336680]  ? lock_acquire+0xb1/0x4a0
[14621.337175]  ? __might_fault+0x3e/0x90
[14621.337707]  ? __x64_sys_io_submit+0x9c/0x330
[14621.338269]  __x64_sys_io_submit+0x9c/0x330
[14621.338812]  ? do_syscall_64+0x5c/0x280
[14621.339303]  do_syscall_64+0x5c/0x280
[14621.339774]  entry_SYSCALL_64_after_hwframe+0x49/0xb3
[14621.340416] RIP: 0033:0x7fb6cd395717
[14621.340875] Code: Bad RIP value.
[14621.341304] RSP: 002b:00007fb6bf7e1de8 EFLAGS: 00000202 ORIG_RAX:
00000000000000d1
[14621.342262] RAX: ffffffffffffffda RBX: 0000560d3d92ea60 RCX: 00007fb6cd395717
[14621.343180] RDX: 0000560d3d92ea60 RSI: 0000000000000008 RDI: 00007fb6cdb32000
[14621.344081] RBP: 0000000000000008 R08: 0000150e50ac6651 R09: 00000000003081a8
[14621.344981] R10: 00007fb6bf7e1df0 R11: 0000000000000202 R12: 0000560d3d8fe110
[14621.345897] R13: 00007fb6bf7e1e10 R14: 00007fb6bf7e1e00 R15: 0000560d3d8fe110
[14621.346820] INFO: lockdep is turned off.
[14742.125500] INFO: task kworker/1:117:15962 blocked for more than 241 seconds.
[14742.126456]       Not tainted 5.7.0-rc7-btrfs-next-59 #1
[14742.127156] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[14742.128156] kworker/1:117   D    0 15962      2 0x80004000
[14742.128875] Workqueue: dio/sdb iomap_dio_complete_work
[14742.129633] Call Trace:
[14742.130010]  __schedule+0x384/0xa30
[14742.130494]  schedule+0x33/0xe0
[14742.131068]  rwsem_down_write_slowpath+0x2c2/0x750
[14742.131956]  ? btrfs_sync_file+0x1fe/0x4d0 [btrfs]
[14742.132834]  btrfs_sync_file+0x1fe/0x4d0 [btrfs]
[14742.133712]  iomap_dio_complete+0x11b/0x260
[14742.134475]  ? aio_fsync_work+0x5b0/0x5b0
[14742.135205]  iomap_dio_complete_work+0x17/0x30
[14742.136018]  process_one_work+0x275/0x6b0
[14742.136677]  worker_thread+0x4f/0x3e0
[14742.137154]  ? process_one_work+0x6b0/0x6b0
[14742.137805]  kthread+0x12a/0x170
[14742.138236]  ? kthread_create_worker_on_cpu+0x70/0x70
[14742.138901]  ret_from_fork+0x3a/0x50
[14742.139389] INFO: task kworker/1:199:16063 blocked for more than 241 seconds.
[14742.140305]       Not tainted 5.7.0-rc7-btrfs-next-59 #1
[14742.140998] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[14742.142056] kworker/1:199   D    0 16063      2 0x80004000
[14742.142877] Workqueue: dio/sdb iomap_dio_complete_work
[14742.143397] Call Trace:
[14742.143654]  __schedule+0x384/0xa30
[14742.144017]  schedule+0x33/0xe0
[14742.144352]  rwsem_down_write_slowpath+0x2c2/0x750
[14742.144859]  ? btrfs_sync_file+0x1fe/0x4d0 [btrfs]
[14742.145386]  btrfs_sync_file+0x1fe/0x4d0 [btrfs]
[14742.145863]  iomap_dio_complete+0x11b/0x260
[14742.146289]  ? aio_fsync_work+0x5b0/0x5b0
[14742.146701]  iomap_dio_complete_work+0x17/0x30
[14742.147168]  process_one_work+0x275/0x6b0
[14742.147579]  worker_thread+0x4f/0x3e0
[14742.147954]  ? process_one_work+0x6b0/0x6b0
[14742.148377]  kthread+0x12a/0x170
[14742.148722]  ? kthread_create_worker_on_cpu+0x70/0x70
[14742.149257]  ret_from_fork+0x3a/0x50
[14742.149671] INFO: task aio-stress:16274 blocked for more than 241 seconds.
[14742.150376]       Not tainted 5.7.0-rc7-btrfs-next-59 #1
[14742.150948] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[14742.151962] aio-stress      D    0 16274  14855 0x00004000
(...)

Thanks.

>
>
> >
> > --
> > Goldwyn
>
>
>
> --
> Filipe David Manana,
>
> “Whether you think you can, or you think you can't — you're right.”



-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”