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

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.