linux-kernel - [PATCH v3] NFS: Fixup allocation flags for nfsiod's __GFP

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Message-ID: <f83ac1155a4bc670f2663959a7a068571e06afd9.1752111622.git.bcodding@redhat.com>
Date: Wed,  9 Jul 2025 21:47:43 -0400
From: Benjamin Coddington <bcodding@...hat.com>
To: 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>,
	Jeff Layton <jlayton@...nel.org>
Subject: [PATCH v3] NFS: Fixup allocation flags for nfsiod's __GFP_NORETRY

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>
Reviewed-by: Jeff Layton <jlayton@...nel.org>
---

	On V3: fix ugly return (Thanks Paulo), add Jeff's R-b
	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..d8f768254f16 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)
+		ret |= __GFP_NORETRY | __GFP_NOWARN;
+	return ret;
 }
 
 /*
-- 
2.47.0