[PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[Qu Wenruo]

[BUG]
There is a bug report that with zoned device and sectorsize is smaller
than page size (aka, subpage), btrfs would crash with a very basic
workload:

 # getconfig PAGESIZE
 16384
 # mkfs.btrfs -f $dev -s 4k
 # mount $dev $mnt
 # $fsstress -w -n 8 -s 1707820327 -v -d $mnt
 # umount $mnt

The crash would look like this (with CONFIG_BTRFS_ASSERT enabled):

 assertion failed: block_start != EXTENT_MAP_HOLE, in fs/btrfs/extent_io.c:1384
 ------------[ cut here ]------------
 kernel BUG at fs/btrfs/extent_io.c:1384!
 CPU: 0 PID: 872 Comm: kworker/u9:2 Tainted: G           OE      6.8.0-rc3-custom+ #7
 Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20231122-12.fc39 11/22/2023
 Workqueue: writeback wb_workfn (flush-btrfs-8)
 pc : __extent_writepage_io+0x404/0x460 [btrfs]
 lr : __extent_writepage_io+0x404/0x460 [btrfs]
 Call trace:
  __extent_writepage_io+0x404/0x460 [btrfs]
  extent_write_locked_range+0x16c/0x460 [btrfs]
  run_delalloc_cow+0x88/0x118 [btrfs]
  btrfs_run_delalloc_range+0x128/0x228 [btrfs]
  writepage_delalloc+0xb8/0x178 [btrfs]
  __extent_writepage+0xc8/0x3a0 [btrfs]
  extent_write_cache_pages+0x1cc/0x460 [btrfs]
  extent_writepages+0x8c/0x120 [btrfs]
  btrfs_writepages+0x18/0x30 [btrfs]
  do_writepages+0x94/0x1f8
  __writeback_single_inode+0x4c/0x388
  writeback_sb_inodes+0x208/0x4b0
  wb_writeback+0x118/0x3c0
  wb_do_writeback+0xbc/0x388
  wb_workfn+0x80/0x240
  process_one_work+0x154/0x3c8
  worker_thread+0x2bc/0x3e0
  kthread+0xf4/0x108
  ret_from_fork+0x10/0x20
 Code: 9102c021 90000be0 91378000 9402bf53 (d4210000)
 ---[ end trace 0000000000000000 ]---

[CAUSE]
There are several factors causing the problem:

1. __extent_writepage_io() requires all dirty ranges to have delalloc
   executed
   This can be solved by adding @start and @len parameter to only submit
   IO for a subset of the page, and update several involved helpers to
   do subpage checks.

   So this is not a big deal.

2. Subpage only accepts for full page aligned ranges for
   extent_write_locked_range()
   For zoned device, regular COW is switched to utilize
   extent_write_locked_range() to submit the IO.

   But the caller, run_delalloc_cow() can be called to run on a subpage
   range, e.g.

   0     4K     8K    12K     16K
   |/////|      |/////|

   Where |///| is the dirtied range.

   In that case, btrfs_run_delalloc_range() would call run_delalloc_cow(),
   which would call extent_write_locked_range() for [0, 4K), and unlock
   the whole [0, 16K) page.

   But btrfs_run_delalloc_range() would again be called for range [8K,
   12K), as there are still dirty range left.
   In that case, since the whole page is already unlocked by previous
   iteration, and would cause different ASSERT()s inside
   extent_write_locked_range().

   That's also why compression for subpage cases require fully page
   aligned range.

[WORKAROUND]
A proper fix requires some big changes to delalloc workload, to allow
extent_write_locked_range() to handle multiple different entries with
the same @locked_page.

So for now, disable read-write support for subpage zoned btrfs.

The problem can only be solved if subpage btrfs can handle subpage
compression, which need quite some work on the delalloc procedure for
the @locked_page handling.

Reported-by: HAN Yuwei <hrx@bupt.moe>
Link: https://lore.kernel.org/all/1ACD2E3643008A17+da260584-2c7f-432a-9e22-9d390aae84cc@bupt.moe/
CC: stable@vger.kernel.org # 5.10+
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/disk-io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index c3ab268533ca..85cd23aebdd6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3193,7 +3193,8 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount)
 	 * part of @locked_page.
 	 * That's also why compression for subpage only work for page aligned ranges.
 	 */
-	if (fs_info->sectorsize < PAGE_SIZE && btrfs_is_zoned(fs_info) && is_rw_mount) {
+	if (fs_info->sectorsize < PAGE_SIZE &&
+	    btrfs_fs_incompat(fs_info, ZONED) && is_rw_mount) {
 		btrfs_warn(fs_info,
 	"no zoned read-write support for page size %lu with sectorsize %u",
 			   PAGE_SIZE, fs_info->sectorsize);
-- 
2.43.0

Re: [PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[Johannes Thumshirn]

On 12.02.24 06:16, Qu Wenruo wrote:
> Reported-by: HAN Yuwei <hrx@bupt.moe>
> Link: https://lore.kernel.org/all/1ACD2E3643008A17+da260584-2c7f-432a-9e22-9d390aae84cc@bupt.moe/
> CC: stable@vger.kernel.org # 5.10+
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/disk-io.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index c3ab268533ca..85cd23aebdd6 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -3193,7 +3193,8 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount)
>   	 * part of @locked_page.
>   	 * That's also why compression for subpage only work for page aligned ranges.
>   	 */
> -	if (fs_info->sectorsize < PAGE_SIZE && btrfs_is_zoned(fs_info) && is_rw_mount) {
> +	if (fs_info->sectorsize < PAGE_SIZE &&
> +	    btrfs_fs_incompat(fs_info, ZONED) && is_rw_mount) {
>   		btrfs_warn(fs_info,
>   	"no zoned read-write support for page size %lu with sectorsize %u",
>   			   PAGE_SIZE, fs_info->sectorsize);

Please keep btrfs_is_zoned(fs_info) instead of using 
btrfs_fs_incompat(fs_info, ZONED).

Otherwise,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Re: [PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[Qu Wenruo]

On 2024/2/12 20:15, Johannes Thumshirn wrote:
> On 12.02.24 06:16, Qu Wenruo wrote:
>> Reported-by: HAN Yuwei <hrx@bupt.moe>
>> Link: https://lore.kernel.org/all/1ACD2E3643008A17+da260584-2c7f-432a-9e22-9d390aae84cc@bupt.moe/
>> CC: stable@vger.kernel.org # 5.10+
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>    fs/btrfs/disk-io.c | 3 ++-
>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index c3ab268533ca..85cd23aebdd6 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -3193,7 +3193,8 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount)
>>    	 * part of @locked_page.
>>    	 * That's also why compression for subpage only work for page aligned ranges.
>>    	 */
>> -	if (fs_info->sectorsize < PAGE_SIZE && btrfs_is_zoned(fs_info) && is_rw_mount) {
>> +	if (fs_info->sectorsize < PAGE_SIZE &&
>> +	    btrfs_fs_incompat(fs_info, ZONED) && is_rw_mount) {
>>    		btrfs_warn(fs_info,
>>    	"no zoned read-write support for page size %lu with sectorsize %u",
>>    			   PAGE_SIZE, fs_info->sectorsize);
>
> Please keep btrfs_is_zoned(fs_info) instead of using
> btrfs_fs_incompat(fs_info, ZONED).

At the time of calling, we haven't yet populate fs_info->zone_size, thus
we have to use super flags to verify if it's zoned.

If needed, I can add a comment for it.

Thanks,
Qu
>
> Otherwise,
> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Re: [PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[Johannes Thumshirn]

On 12.02.24 10:50, Qu Wenruo wrote:
> 
> 
> On 2024/2/12 20:15, Johannes Thumshirn wrote:
>> On 12.02.24 06:16, Qu Wenruo wrote:
>>> Reported-by: HAN Yuwei <hrx@bupt.moe>
>>> Link: https://lore.kernel.org/all/1ACD2E3643008A17+da260584-2c7f-432a-9e22-9d390aae84cc@bupt.moe/
>>> CC: stable@vger.kernel.org # 5.10+
>>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>>> ---
>>>     fs/btrfs/disk-io.c | 3 ++-
>>>     1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>>> index c3ab268533ca..85cd23aebdd6 100644
>>> --- a/fs/btrfs/disk-io.c
>>> +++ b/fs/btrfs/disk-io.c
>>> @@ -3193,7 +3193,8 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount)
>>>     	 * part of @locked_page.
>>>     	 * That's also why compression for subpage only work for page aligned ranges.
>>>     	 */
>>> -	if (fs_info->sectorsize < PAGE_SIZE && btrfs_is_zoned(fs_info) && is_rw_mount) {
>>> +	if (fs_info->sectorsize < PAGE_SIZE &&
>>> +	    btrfs_fs_incompat(fs_info, ZONED) && is_rw_mount) {
>>>     		btrfs_warn(fs_info,
>>>     	"no zoned read-write support for page size %lu with sectorsize %u",
>>>     			   PAGE_SIZE, fs_info->sectorsize);
>>
>> Please keep btrfs_is_zoned(fs_info) instead of using
>> btrfs_fs_incompat(fs_info, ZONED).
> 
> At the time of calling, we haven't yet populate fs_info->zone_size, thus
> we have to use super flags to verify if it's zoned.
> 
> If needed, I can add a comment for it.

All good, I didn't have enough coffee.

Re: [PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[David Sterba]

On Mon, Feb 12, 2024 at 08:20:21PM +1030, Qu Wenruo wrote:
> 
> 
> On 2024/2/12 20:15, Johannes Thumshirn wrote:
> > On 12.02.24 06:16, Qu Wenruo wrote:
> >> Reported-by: HAN Yuwei <hrx@bupt.moe>
> >> Link: https://lore.kernel.org/all/1ACD2E3643008A17+da260584-2c7f-432a-9e22-9d390aae84cc@bupt.moe/
> >> CC: stable@vger.kernel.org # 5.10+
> >> Signed-off-by: Qu Wenruo <wqu@suse.com>
> >> ---
> >>    fs/btrfs/disk-io.c | 3 ++-
> >>    1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> >> index c3ab268533ca..85cd23aebdd6 100644
> >> --- a/fs/btrfs/disk-io.c
> >> +++ b/fs/btrfs/disk-io.c
> >> @@ -3193,7 +3193,8 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount)
> >>    	 * part of @locked_page.
> >>    	 * That's also why compression for subpage only work for page aligned ranges.
> >>    	 */
> >> -	if (fs_info->sectorsize < PAGE_SIZE && btrfs_is_zoned(fs_info) && is_rw_mount) {
> >> +	if (fs_info->sectorsize < PAGE_SIZE &&
> >> +	    btrfs_fs_incompat(fs_info, ZONED) && is_rw_mount) {
> >>    		btrfs_warn(fs_info,
> >>    	"no zoned read-write support for page size %lu with sectorsize %u",
> >>    			   PAGE_SIZE, fs_info->sectorsize);
> >
> > Please keep btrfs_is_zoned(fs_info) instead of using
> > btrfs_fs_incompat(fs_info, ZONED).
> 
> At the time of calling, we haven't yet populate fs_info->zone_size, thus
> we have to use super flags to verify if it's zoned.
> 
> If needed, I can add a comment for it.

Yes please add a comment the difference is quite subtle.

Re: [PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[Qu Wenruo]

在 2024/2/14 17:59, David Sterba 写道:
> On Mon, Feb 12, 2024 at 08:20:21PM +1030, Qu Wenruo wrote:
>>
>>
>> On 2024/2/12 20:15, Johannes Thumshirn wrote:
>>> On 12.02.24 06:16, Qu Wenruo wrote:
>>>> Reported-by: HAN Yuwei <hrx@bupt.moe>
>>>> Link: https://lore.kernel.org/all/1ACD2E3643008A17+da260584-2c7f-432a-9e22-9d390aae84cc@bupt.moe/
>>>> CC: stable@vger.kernel.org # 5.10+
>>>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>>>> ---
>>>>     fs/btrfs/disk-io.c | 3 ++-
>>>>     1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>>>> index c3ab268533ca..85cd23aebdd6 100644
>>>> --- a/fs/btrfs/disk-io.c
>>>> +++ b/fs/btrfs/disk-io.c
>>>> @@ -3193,7 +3193,8 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount)
>>>>     	 * part of @locked_page.
>>>>     	 * That's also why compression for subpage only work for page aligned ranges.
>>>>     	 */
>>>> -	if (fs_info->sectorsize < PAGE_SIZE && btrfs_is_zoned(fs_info) && is_rw_mount) {
>>>> +	if (fs_info->sectorsize < PAGE_SIZE &&
>>>> +	    btrfs_fs_incompat(fs_info, ZONED) && is_rw_mount) {
>>>>     		btrfs_warn(fs_info,
>>>>     	"no zoned read-write support for page size %lu with sectorsize %u",
>>>>     			   PAGE_SIZE, fs_info->sectorsize);
>>>
>>> Please keep btrfs_is_zoned(fs_info) instead of using
>>> btrfs_fs_incompat(fs_info, ZONED).
>>
>> At the time of calling, we haven't yet populate fs_info->zone_size, thus
>> we have to use super flags to verify if it's zoned.
>>
>> If needed, I can add a comment for it.
>
> Yes please add a comment the difference is quite subtle.
>

I'd say this patch can be dropped.

The reason is:

- I'm already working on the proper subpage handling for the
   @locked_page of a delalloc range

   The patchset is under testing now, the results looks fine for
   both regular and subpage cases.
   Will queue extra testing for subpage zoned.

- The rejection would cause future problems for detecting whether we
   have proper subpage + zoned support.
   Either we do not detect, or introduce a complex mechanism only for
   this one edge case.

   Thus I prefer not to detect.

- Subage + zoned is too niche for now
   The most common subpage usage would be aarch64 (especially for Apple
   M1/2 chips).
   For those Apple based ones, they have no ability to expand, thus won't
   hit any real zoned devices.
   For other aarch64 servers, they should have the ability to choose a 4K
   page size kernel if they really want to go zoned devices.

   This bug is only exposed with a helpful reporter using 16K page sized
   loongson board with SATA zoned disk.

Due to above reasons, I really prefer to keep the current situation, and
focus on the proper fix instead.

Thanks,
Qu

Re: [PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[David Sterba]

On Mon, Feb 12, 2024 at 03:46:15PM +1030, Qu Wenruo wrote:
> [BUG]
> There is a bug report that with zoned device and sectorsize is smaller
> than page size (aka, subpage), btrfs would crash with a very basic
> workload:
> 
>  # getconfig PAGESIZE
>  16384
>  # mkfs.btrfs -f $dev -s 4k
>  # mount $dev $mnt
>  # $fsstress -w -n 8 -s 1707820327 -v -d $mnt
>  # umount $mnt
> 
> The crash would look like this (with CONFIG_BTRFS_ASSERT enabled):
> 
>  assertion failed: block_start != EXTENT_MAP_HOLE, in fs/btrfs/extent_io.c:1384

This is the same as what Josef fixed in
https://github.com/btrfs/linux/commit/400bb013912dac637c7d6826407be580ea8ef9cc
"btrfs: don't drop extent_map for free space inode on write error"
but not on zoned+subpage, is it really a different error you're fixing?

[...]
> [WORKAROUND]
> A proper fix requires some big changes to delalloc workload, to allow
> extent_write_locked_range() to handle multiple different entries with
> the same @locked_page.
> 
> So for now, disable read-write support for subpage zoned btrfs.
> 
> The problem can only be solved if subpage btrfs can handle subpage
> compression, which need quite some work on the delalloc procedure for
> the @locked_page handling.

Ok, this on itself is a valid reason to disable the support.

Re: [PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[Qu Wenruo]

[-- Attachment #1.1.1: Type: text/plain, Size: 2379 bytes --]



On 2024/2/12 21:44, David Sterba wrote:
> On Mon, Feb 12, 2024 at 03:46:15PM +1030, Qu Wenruo wrote:
>> [BUG]
>> There is a bug report that with zoned device and sectorsize is smaller
>> than page size (aka, subpage), btrfs would crash with a very basic
>> workload:
>>
>>   # getconfig PAGESIZE
>>   16384
>>   # mkfs.btrfs -f $dev -s 4k
>>   # mount $dev $mnt
>>   # $fsstress -w -n 8 -s 1707820327 -v -d $mnt
>>   # umount $mnt
>>
>> The crash would look like this (with CONFIG_BTRFS_ASSERT enabled):
>>
>>   assertion failed: block_start != EXTENT_MAP_HOLE, in fs/btrfs/extent_io.c:1384
> 
> This is the same as what Josef fixed in
> https://github.com/btrfs/linux/commit/400bb013912dac637c7d6826407be580ea8ef9cc
> "btrfs: don't drop extent_map for free space inode on write error"
> but not on zoned+subpage, is it really a different error you're fixing?

Yes, it's really a different bug.

Although the root cause is a little more complex, it has to be explained 
through the whole CAUSE section.

> 
> [...]
>> [WORKAROUND]
>> A proper fix requires some big changes to delalloc workload, to allow
>> extent_write_locked_range() to handle multiple different entries with
>> the same @locked_page.
>>
>> So for now, disable read-write support for subpage zoned btrfs.
>>
>> The problem can only be solved if subpage btrfs can handle subpage
>> compression, which need quite some work on the delalloc procedure for
>> the @locked_page handling.
> 
> Ok, this on itself is a valid reason to disable the support.

But this reminds me that, I have to work on the proper delalloc support 
for subpage.

My current plan is:

1. Introduce subpage LOCK bitmap
    Not just only an atomic counter.

2. Make find_lock_delalloc_range() to populate that lock bitmap

3. Make find_lock_delalloc_range() to find all delalloc range of
    a page and properly lock them
    This would not change the behavior for page sized sectorsize.

4. Make find_lock_delalloc_range() to skip the page if it's already
    being locked before.
    This is also a subpage specific behavior

With above planned work, btrfs should be able to handle subpage unlock, 
so that we won't need weird @locked_page handling.

Hopefully this would solve both the subpage+zoned and full sector 
aligned subpage compression support.

Thanks,
Qu

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Re: [PATCH] btrfs: reject zoned RW mount if sectorsize is smaller than page size

[David Sterba]

On Mon, Feb 12, 2024 at 03:46:15PM +1030, Qu Wenruo wrote:
> [BUG]
> There is a bug report that with zoned device and sectorsize is smaller
> than page size (aka, subpage), btrfs would crash with a very basic
> workload:
> 
>  # getconfig PAGESIZE
>  16384
>  # mkfs.btrfs -f $dev -s 4k
>  # mount $dev $mnt
>  # $fsstress -w -n 8 -s 1707820327 -v -d $mnt
>  # umount $mnt
> 
> The crash would look like this (with CONFIG_BTRFS_ASSERT enabled):
> 
>  assertion failed: block_start != EXTENT_MAP_HOLE, in fs/btrfs/extent_io.c:1384
>  ------------[ cut here ]------------
>  kernel BUG at fs/btrfs/extent_io.c:1384!
>  CPU: 0 PID: 872 Comm: kworker/u9:2 Tainted: G           OE      6.8.0-rc3-custom+ #7
>  Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20231122-12.fc39 11/22/2023
>  Workqueue: writeback wb_workfn (flush-btrfs-8)
>  pc : __extent_writepage_io+0x404/0x460 [btrfs]
>  lr : __extent_writepage_io+0x404/0x460 [btrfs]
>  Call trace:
>   __extent_writepage_io+0x404/0x460 [btrfs]
>   extent_write_locked_range+0x16c/0x460 [btrfs]
>   run_delalloc_cow+0x88/0x118 [btrfs]
>   btrfs_run_delalloc_range+0x128/0x228 [btrfs]
>   writepage_delalloc+0xb8/0x178 [btrfs]
>   __extent_writepage+0xc8/0x3a0 [btrfs]
>   extent_write_cache_pages+0x1cc/0x460 [btrfs]
>   extent_writepages+0x8c/0x120 [btrfs]
>   btrfs_writepages+0x18/0x30 [btrfs]
>   do_writepages+0x94/0x1f8
>   __writeback_single_inode+0x4c/0x388
>   writeback_sb_inodes+0x208/0x4b0
>   wb_writeback+0x118/0x3c0
>   wb_do_writeback+0xbc/0x388
>   wb_workfn+0x80/0x240
>   process_one_work+0x154/0x3c8
>   worker_thread+0x2bc/0x3e0
>   kthread+0xf4/0x108
>   ret_from_fork+0x10/0x20
>  Code: 9102c021 90000be0 91378000 9402bf53 (d4210000)
>  ---[ end trace 0000000000000000 ]---
> 
> [CAUSE]
> There are several factors causing the problem:
> 
> 1. __extent_writepage_io() requires all dirty ranges to have delalloc
>    executed
>    This can be solved by adding @start and @len parameter to only submit
>    IO for a subset of the page, and update several involved helpers to
>    do subpage checks.
> 
>    So this is not a big deal.
> 
> 2. Subpage only accepts for full page aligned ranges for
>    extent_write_locked_range()
>    For zoned device, regular COW is switched to utilize
>    extent_write_locked_range() to submit the IO.
> 
>    But the caller, run_delalloc_cow() can be called to run on a subpage
>    range, e.g.
> 
>    0     4K     8K    12K     16K
>    |/////|      |/////|
> 
>    Where |///| is the dirtied range.
> 
>    In that case, btrfs_run_delalloc_range() would call run_delalloc_cow(),
>    which would call extent_write_locked_range() for [0, 4K), and unlock
>    the whole [0, 16K) page.
> 
>    But btrfs_run_delalloc_range() would again be called for range [8K,
>    12K), as there are still dirty range left.
>    In that case, since the whole page is already unlocked by previous
>    iteration, and would cause different ASSERT()s inside
>    extent_write_locked_range().
> 
>    That's also why compression for subpage cases require fully page
>    aligned range.
> 
> [WORKAROUND]
> A proper fix requires some big changes to delalloc workload, to allow
> extent_write_locked_range() to handle multiple different entries with
> the same @locked_page.
> 
> So for now, disable read-write support for subpage zoned btrfs.
> 
> The problem can only be solved if subpage btrfs can handle subpage
> compression, which need quite some work on the delalloc procedure for
> the @locked_page handling.
> 
> Reported-by: HAN Yuwei <hrx@bupt.moe>
> Link: https://lore.kernel.org/all/1ACD2E3643008A17+da260584-2c7f-432a-9e22-9d390aae84cc@bupt.moe/
> CC: stable@vger.kernel.org # 5.10+
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/disk-io.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index c3ab268533ca..85cd23aebdd6 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -3193,7 +3193,8 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount)
>  	 * part of @locked_page.
>  	 * That's also why compression for subpage only work for page aligned ranges.
>  	 */
> -	if (fs_info->sectorsize < PAGE_SIZE && btrfs_is_zoned(fs_info) && is_rw_mount) {
> +	if (fs_info->sectorsize < PAGE_SIZE &&
> +	    btrfs_fs_incompat(fs_info, ZONED) && is_rw_mount) {
>  		btrfs_warn(fs_info,
>  	"no zoned read-write support for page size %lu with sectorsize %u",
>  			   PAGE_SIZE, fs_info->sectorsize);

This does not match any code I see in usual branches and it also does
not apply so it can't be picked as a fix.