Re: [PATCH] xfs: use GFP_NOFS in __xfs_trans_alloc

[Darrick J. Wong]

On Thu, Mar 12, 2026 at 03:22:14PM +0800, Morduan Zang wrote:
> __xfs_trans_alloc() allocates the transaction structure before
> xfs_trans_set_context() establishes the nofs context. If memory reclaim
> enters XFS through xfs_vn_sync_lazytime(), this GFP_KERNEL allocation can
> trigger a warning from the reclaim path.
> 
> Use GFP_NOFS for the transaction allocation to avoid filesystem reclaim
> recursion before the nofs context is set.

Why doesn't filesystem reclaim itself set PF_MEMALLOC_NOFS for us?

 xfs_vn_sync_lazytime+0xaf/0x150 fs/xfs/xfs_iops.c:1238
 sync_lazytime+0x12d/0x2d0 fs/fs-writeback.c:1721
 iput+0x230/0xe80 fs/inode.c:1997
 __dentry_kill+0x1a2/0x5e0 fs/dcache.c:670
 shrink_kill+0xa9/0x2c0 fs/dcache.c:1147
 shrink_dentry_list+0x2e0/0x5e0 fs/dcache.c:1174
 prune_dcache_sb+0x119/0x180 fs/dcache.c:1256
 super_cache_scan+0x369/0x4b0 fs/super.c:223
 do_shrink_slab+0x6df/0x1170 mm/shrinker.c:437`

--D

> Link: https://syzkaller.appspot.com/bug?extid=d78ace33ad4ee69329d5
> Fixes: 83a80e95e797 ("xfs: decouple xfs_trans_alloc_empty from xfs_trans_alloc")
> Reported-by: syzbot+d78ace33ad4ee69329d5@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> Signed-off-by: Zhan Jun <zhanjun@xxxxxxxxxxxxx>
> Signed-off-by: Morduan Zang <zhangdandan@xxxxxxxxxxxxx>
> ---
>  fs/xfs/xfs_trans.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index bcc470f56e46..0d347cff7317 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -217,7 +217,7 @@ __xfs_trans_alloc(
>  
>  	ASSERT(!(flags & XFS_TRANS_RES_FDBLKS) || xfs_has_lazysbcount(mp));
>  
> -	tp = kmem_cache_zalloc(xfs_trans_cache, GFP_KERNEL | __GFP_NOFAIL);
> +	tp = kmem_cache_zalloc(xfs_trans_cache, GFP_NOFS | __GFP_NOFAIL);
>  	if (!(flags & XFS_TRANS_NO_WRITECOUNT))
>  		sb_start_intwrite(mp->m_super);
>  	xfs_trans_set_context(tp);
> -- 
> 2.50.1
> 
>