Patch "nfsd: Set PF_LOCAL_THROTTLE on local filesystems only" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    nfsd: Set PF_LOCAL_THROTTLE on local filesystems only

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfsd-set-pf_local_throttle-on-local-filesystems-only.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c8cc4e81cf3ac5a58ed7dea390b4c4bef07a2941
Author: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Date:   Mon Nov 30 17:03:19 2020 -0500

    nfsd: Set PF_LOCAL_THROTTLE on local filesystems only
    
    [ Upstream commit 01cbf3853959feec40ec9b9a399e12a021cd4d81 ]
    
    Don't set PF_LOCAL_THROTTLE on remote filesystems like NFS, since they
    aren't expected to ever be subject to double buffering.
    
    Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/nfs/export.c b/fs/nfs/export.c
index 5428713af5fee..48b879cfe6e3b 100644
--- a/fs/nfs/export.c
+++ b/fs/nfs/export.c
@@ -171,5 +171,6 @@ const struct export_operations nfs_export_ops = {
 	.encode_fh = nfs_encode_fh,
 	.fh_to_dentry = nfs_fh_to_dentry,
 	.get_parent = nfs_get_parent,
-	.flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|EXPORT_OP_CLOSE_BEFORE_UNLINK,
+	.flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|
+		EXPORT_OP_CLOSE_BEFORE_UNLINK|EXPORT_OP_REMOTE_FS,
 };
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index fb4e6c57ce0bb..a515cbd0a7d8f 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -986,6 +986,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 				__be32 *verf)
 {
 	struct file		*file = nf->nf_file;
+	struct super_block	*sb = file_inode(file)->i_sb;
 	struct svc_export	*exp;
 	struct iov_iter		iter;
 	errseq_t		since;
@@ -993,12 +994,18 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 	int			host_err;
 	int			use_wgather;
 	loff_t			pos = offset;
+	unsigned long		exp_op_flags = 0;
 	unsigned int		pflags = current->flags;
 	rwf_t			flags = 0;
+	bool			restore_flags = false;
 
 	trace_nfsd_write_opened(rqstp, fhp, offset, *cnt);
 
-	if (test_bit(RQ_LOCAL, &rqstp->rq_flags))
+	if (sb->s_export_op)
+		exp_op_flags = sb->s_export_op->flags;
+
+	if (test_bit(RQ_LOCAL, &rqstp->rq_flags) &&
+	    !(exp_op_flags & EXPORT_OP_REMOTE_FS)) {
 		/*
 		 * We want throttling in balance_dirty_pages()
 		 * and shrink_inactive_list() to only consider
@@ -1007,6 +1014,8 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 		 * the client's dirty pages or its congested queue.
 		 */
 		current->flags |= PF_LOCAL_THROTTLE;
+		restore_flags = true;
+	}
 
 	exp = fhp->fh_export;
 	use_wgather = (rqstp->rq_vers == 2) && EX_WGATHER(exp);
@@ -1062,7 +1071,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf,
 		trace_nfsd_write_err(rqstp, fhp, offset, host_err);
 		nfserr = nfserrno(host_err);
 	}
-	if (test_bit(RQ_LOCAL, &rqstp->rq_flags))
+	if (restore_flags)
 		current_restore_flags(pflags, PF_LOCAL_THROTTLE);
 	return nfserr;
 }
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 846df3c96730f..d93e8a6737bb0 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -216,6 +216,7 @@ struct export_operations {
 #define	EXPORT_OP_NOWCC			(0x1) /* don't collect v3 wcc data */
 #define	EXPORT_OP_NOSUBTREECHK		(0x2) /* no subtree checking */
 #define	EXPORT_OP_CLOSE_BEFORE_UNLINK	(0x4) /* close files before unlink */
+#define EXPORT_OP_REMOTE_FS		(0x8) /* Filesystem is remote */
 	unsigned long	flags;
 };