linux-kernel - Re: [PATCH v2] NFS: Fixup allocation flags for nfsiod's __GFP

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Message-ID: <b2743a19cf1db829c8702a4eeadef0f6cc09d2c0.camel@kernel.org>
Date: Wed, 09 Jul 2025 15:32:47 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Benjamin Coddington <bcodding@...hat.com>, Trond Myklebust
	 <trondmy@...nel.org>, Anna Schumaker <anna@...nel.org>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org, Laurence
 Oberman	 <loberman@...hat.com>
Subject: Re: [PATCH v2] NFS: Fixup allocation flags for nfsiod's
 __GFP_NORETRY

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@...nel.org>
> Fixes: 0bae835b63c5 ("NFS: Avoid writeback threads getting stuck in mempool_alloc()")
> Signed-off-by: Benjamin Coddington <bcodding@...hat.com>
> Reviewed-by: Laurence Oberman <loberman@...hat.com>
> Tested-by: Laurence Oberman <loberman@...hat.com>
> ---
> 
> 	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@...nel.org>