On Tue, Feb 16, 2021 at 2:25 PM David Sterba [off-list ref] wrote:

On Mon, Feb 15, 2021 at 11:05:33AM +0000, Filipe Manana wrote:

quoted

On Sat, Feb 13, 2021 at 1:07 AM Wang Yugui [off-list ref] wrote:

quoted

quoted

This bug only affects 5.10 kernels, and the regression was introduced in
5.10-rc1 by commit 0eb79294dbe328 ("btrfs: dio iomap DSYNC workaround").
The bug does not exist in 5.11 kernels due to commit ecfdc08b8cc65d
("btrfs: remove dio iomap DSYNC workaround"), which depends on other
changes that went into the merge window for 5.11. So this is a fix only
for 5.10.x stable kernels, as there are people hitting this.

It is OK too to backport commit ecfdc08b8cc65d
 ("btrfs: remove dio iomap DSYNC workaround") to 5.10 for this problem?

the iomap issue for commit 0eb79294dbe328 ("btrfs: dio iomap DSYNC workaround")
is already fixed in 5.10?

Quoting the changelog:

"commit ecfdc08b8cc65d
("btrfs: remove dio iomap DSYNC workaround"), which depends on other
changes that went into the merge window for 5.11."

All the changes, are (at least):

commit ecfdc08b8cc65d737eebc26a1ee1875a097fd6a0   --> 5.11-rc1
Author: Goldwyn Rodrigues [off-list ref]
Date:   Thu Sep 24 11:39:21 2020 -0500

    btrfs: remove dio iomap DSYNC workaround

commit a42fa643169d2325602572633fcaa16862990e28
Author: Goldwyn Rodrigues [off-list ref]
Date:   Thu Sep 24 11:39:20 2020 -0500

    btrfs: call iomap_dio_complete() without inode_lock

commit 502756b380938022c848761837f8fa3976906aa1
Author: Goldwyn Rodrigues [off-list ref]
Date:   Thu Sep 24 11:39:19 2020 -0500

    btrfs: remove btrfs_inode::dio_sem

commit e9adabb9712ef9424cbbeeaa027d962ab5262e19
Author: Goldwyn Rodrigues [off-list ref]
Date:   Thu Sep 24 11:39:18 2020 -0500

    btrfs: use shared lock for direct writes within EOF

commit c352370633400d13765cc88080c969799ea51108
Author: Goldwyn Rodrigues [off-list ref]
Date:   Thu Sep 24 11:39:17 2020 -0500

    btrfs: push inode locking and unlocking into buffered/direct write

commit a14b78ad06aba0fa7e76d2bc13c5ba581a7f331a
Author: Goldwyn Rodrigues [off-list ref]
Date:   Thu Sep 24 11:39:16 2020 -0500

    btrfs: introduce btrfs_inode_lock()/unlock()

commit b8d8e1fd570a194904f545b135efc880d96a41a4
Author: Goldwyn Rodrigues [off-list ref]
Date:   Thu Sep 24 11:39:15 2020 -0500

    btrfs: introduce btrfs_write_check()

That's probably too much to add to stable at once, plus I'm assuming
all required iomap dependencies are in 5.10 already (it seems so,
unless I missed something).

Usually we don't add patches to stable that didn't go through Linus'
tree either (there were 1 or 2 very rare exceptions in the past I
think), but when a backport depends on so many patches, and not all
from the same patchset, the risk of getting something wrong is
significant. That's why I opted to send this patch, which is much more
simple.

Agreed, in this case the backport would be too big, just the diffstat
between b8d8e1fd570^..ecfdc08b8cc6 is

 5 files changed, 213 insertions(+), 240 deletions(-)

This fix is minimal and suitable for stable as an exception. You did not
CC stable@vger.kernel.org so you'll need to send it again. Please CC me
too in case there are some questions from stable team. Thanks.

Ah yes, my usual script to send patches suppresses all cc by default,
I missed that.
Ok, sent again. Thanks.