[PATCH] btrfs: fix double-decrement of bytes_may_use in submit_one_async_extent()

[PATCH] btrfs: fix double-decrement of bytes_may_use in submit_one_async_extent()

[Mark Harmstone]

submit_one_async_extent() calls btrfs_reserve_extent(), which decrements
bytes_may_use. If the call btrfs_create_io_em() fails, we jump to
out_free_reserve, which calls extent_clear_unlock_delalloc().

Because we're specifying EXTENT_DO_ACCOUNTING, i.e.
EXTENT_CLEAR_META_RESV | EXTENT_CLEAR_DATA_RESV, this decreases
bytes_may_use again. This can lead to problems later on, as an initial
write can fail only for the writeback to silently ENOSPC.

Fix this by replacing EXTENT_DO_ACCOUNTING with EXTENT_CLEAR_META_RESV.
This parallels a4fe134fc1d8, which is the same fix in cow_one_range().

Fixes: 151a41bc46df ("Btrfs: fix what bits we clear when erroring out from delalloc")
Signed-off-by: Mark Harmstone <mark@harmstone.com>
---
 fs/btrfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 36bbf2297a9987..abedaeb45189a2 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1204,7 +1204,7 @@ static void submit_one_async_extent(struct async_chunk *async_chunk,
 				     NULL, &cached,
 				     EXTENT_LOCKED | EXTENT_DELALLOC |
 				     EXTENT_DELALLOC_NEW |
-				     EXTENT_DEFRAG | EXTENT_DO_ACCOUNTING,
+				     EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV,
 				     PAGE_UNLOCK | PAGE_START_WRITEBACK |
 				     PAGE_END_WRITEBACK);
 	if (async_extent->cb)
-- 
2.52.0

Re: [PATCH] btrfs: fix double-decrement of bytes_may_use in submit_one_async_extent()

[Qu Wenruo]

在 2026/4/17 03:13, Mark Harmstone 写道:
> submit_one_async_extent() calls btrfs_reserve_extent(), which decrements
> bytes_may_use. If the call btrfs_create_io_em() fails, we jump to
> out_free_reserve, which calls extent_clear_unlock_delalloc().
> 
> Because we're specifying EXTENT_DO_ACCOUNTING, i.e.
> EXTENT_CLEAR_META_RESV | EXTENT_CLEAR_DATA_RESV, this decreases
> bytes_may_use again. This can lead to problems later on, as an initial
> write can fail only for the writeback to silently ENOSPC.
> 
> Fix this by replacing EXTENT_DO_ACCOUNTING with EXTENT_CLEAR_META_RESV.
> This parallels a4fe134fc1d8, which is the same fix in cow_one_range().
> 
> Fixes: 151a41bc46df ("Btrfs: fix what bits we clear when erroring out from delalloc")
> Signed-off-by: Mark Harmstone <mark@harmstone.com>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu

> ---
>   fs/btrfs/inode.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 36bbf2297a9987..abedaeb45189a2 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -1204,7 +1204,7 @@ static void submit_one_async_extent(struct async_chunk *async_chunk,
>   				     NULL, &cached,
>   				     EXTENT_LOCKED | EXTENT_DELALLOC |
>   				     EXTENT_DELALLOC_NEW |
> -				     EXTENT_DEFRAG | EXTENT_DO_ACCOUNTING,
> +				     EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV,
>   				     PAGE_UNLOCK | PAGE_START_WRITEBACK |
>   				     PAGE_END_WRITEBACK);
>   	if (async_extent->cb)

Re: [PATCH] btrfs: fix double-decrement of bytes_may_use in submit_one_async_extent()

[David Sterba]

On Thu, Apr 16, 2026 at 06:43:51PM +0100, Mark Harmstone wrote:
> submit_one_async_extent() calls btrfs_reserve_extent(), which decrements
> bytes_may_use. If the call btrfs_create_io_em() fails, we jump to
> out_free_reserve, which calls extent_clear_unlock_delalloc().
> 
> Because we're specifying EXTENT_DO_ACCOUNTING, i.e.
> EXTENT_CLEAR_META_RESV | EXTENT_CLEAR_DATA_RESV, this decreases
> bytes_may_use again. This can lead to problems later on, as an initial
> write can fail only for the writeback to silently ENOSPC.
> 
> Fix this by replacing EXTENT_DO_ACCOUNTING with EXTENT_CLEAR_META_RESV.
> This parallels a4fe134fc1d8, which is the same fix in cow_one_range().
                 ^^^^^^^^^^^^

Please for first occurence put the full commit reference, the same one
as for the Fixes tag. Fixed in for-next.