On Wed, 2025-07-09 at 10:48 -0400, Benjamin Coddington wrote:
> If the NFS client is doing writeback from a workqueue context, avoid using
> __GFP_NORETRY for allocations if the task has set PF_MEMALLOC_NOIO or
> PF_MEMALLOC_NOFS. The combination of these flags makes memory allocation
> failures much more likely.
>
> We've seen those allocation failures show up when the loopback driver is
> doing writeback from a workqueue to a file on NFS, where memory allocation
> failure results in errors or corruption within the loopback device's
> filesystem.
>
> Suggested-by: Trond Myklebust <trondmy@xxxxxxxxxx>
> Fixes: 0bae835b63c5 ("NFS: Avoid writeback threads getting stuck in mempool_alloc()")
> Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
> Reviewed-by: Laurence Oberman <loberman@xxxxxxxxxx>
> Tested-by: Laurence Oberman <loberman@xxxxxxxxxx>
> ---
>
> On V2: add missing 'Fixes' and Laurence's R-b T-b
>
> fs/nfs/internal.h | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
> index 69c2c10ee658..7f3213607431 100644
> --- a/fs/nfs/internal.h
> +++ b/fs/nfs/internal.h
> @@ -671,9 +671,12 @@ nfs_write_match_verf(const struct nfs_writeverf *verf,
>
> static inline gfp_t nfs_io_gfp_mask(void)
> {
> - if (current->flags & PF_WQ_WORKER)
> - return GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
> - return GFP_KERNEL;
> + gfp_t ret = current_gfp_context(GFP_KERNEL);
> +
> + /* For workers __GFP_NORETRY only with __GFP_IO or __GFP_FS */
> + if ((current->flags & PF_WQ_WORKER) && ret == GFP_KERNEL)
> + return ret |= __GFP_NORETRY | __GFP_NOWARN;
> + return ret;
> }
>
> /*
This way works too!
Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
