From 074d7306a4fe22fcac0b53f699f92757ab1cee99 Mon Sep 17 00:00:00 2001
From: Andreas Gruenbacher <agruenba@redhat.com>
Date: Mon, 30 Oct 2023 22:06:05 +0100
Subject: [PATCH] gfs2: Silence "suspicious RCU usage in gfs2_permission"
 warning
Git-commit: 074d7306a4fe22fcac0b53f699f92757ab1cee99
Patch-mainline: v6.7-rc1
References: git-fixes

Commit 0abd1557e21c added rcu_dereference() for dereferencing ip->i_gl
in gfs2_permission.  This now causes lockdep to complain when
gfs2_permission is called in non-RCU context:

    WARNING: suspicious RCU usage in gfs2_permission

Switch to rcu_dereference_check() and check for the MAY_NOT_BLOCK flag
to shut up lockdep when we know that dereferencing ip->i_gl is safe.

Fixes: 0abd1557e21c ("gfs2: fix an oops in gfs2_permission")
Reported-by: syzbot+3e5130844b0c0e2b4948@syzkaller.appspotmail.com
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Acked-by: Anthony Iliopoulos <ailiop@suse.com>

---
 fs/gfs2/inode.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -1848,6 +1848,7 @@ out:
 int gfs2_permission(struct user_namespace *mnt_userns, struct inode *inode,
 		    int mask)
 {
+	int may_not_block = mask & MAY_NOT_BLOCK;
 	struct gfs2_inode *ip;
 	struct gfs2_holder i_gh;
 	struct gfs2_glock *gl;
@@ -1855,14 +1856,14 @@ int gfs2_permission(struct user_namespac
 
 	gfs2_holder_mark_uninitialized(&i_gh);
 	ip = GFS2_I(inode);
-	gl = rcu_dereference(ip->i_gl);
+	gl = rcu_dereference_check(ip->i_gl, !may_not_block);
 	if (unlikely(!gl)) {
 		/* inode is getting torn down, must be RCU mode */
-		WARN_ON_ONCE(!(mask & MAY_NOT_BLOCK));
+		WARN_ON_ONCE(!may_not_block);
 		return -ECHILD;
         }
 	if (gfs2_glock_is_locked_by_me(gl) == NULL) {
-		if (mask & MAY_NOT_BLOCK)
+		if (may_not_block)
 			return -ECHILD;
 		error = gfs2_glock_nq_init(gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
 		if (error)