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@kernel.org>
Fixes: 0bae835 ("NFS: Avoid writeback threads getting stuck in mempool_alloc()")
Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/f83ac1155a4bc670f2663959a7a068571e06afd9.1752111622.git.bcodding@redhat.com
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: bcodding-rh

fs/nfs/internal.h

@@ -670,9 +670,12 @@ 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;
 }
 
 /*