ovl: drop WARN_ON() dentry is NULL in ovl_encode_fh()

stable inclusion
from stable-v5.10.137
commit 542d2e799d53577b961f74914342c9e972c3f1ab
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=542d2e799d53577b961f74914342c9e972c3f1ab

--------------------------------

commit dd524b7f upstream.

Some code paths cannot guarantee the inode have any dentry alias. So
WARN_ON() all !dentry may flood the kernel logs.

For example, when an overlayfs inode is watched by inotifywait (1), and
someone is trying to read the /proc/$(pidof inotifywait)/fdinfo/INOTIFY_FD,
at that time if the dentry has been reclaimed by kernel (such as
echo 2 > /proc/sys/vm/drop_caches), there will be a WARN_ON(). The
printed call stack would be like:

    ? show_mark_fhandle+0xf0/0xf0
    show_mark_fhandle+0x4a/0xf0
    ? show_mark_fhandle+0xf0/0xf0
    ? seq_vprintf+0x30/0x50
    ? seq_printf+0x53/0x70
    ? show_mark_fhandle+0xf0/0xf0
    inotify_fdinfo+0x70/0x90
    show_fdinfo.isra.4+0x53/0x70
    seq_show+0x130/0x170
    seq_read+0x153/0x440
    vfs_read+0x94/0x150
    ksys_read+0x5f/0xe0
    do_syscall_64+0x59/0x1e0
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

So let's drop WARN_ON() to avoid kernel log flooding.
Reported-by: NHongbo Yin <yinhongbo@bytedance.com>
Signed-off-by: NJiachen Zhang <zhangjiachen.jaycee@bytedance.com>
Signed-off-by: NTianci Zhang <zhangtianci.1997@bytedance.com>
Fixes: 8ed5eec9 ("ovl: encode pure upper file handles")
Cc: <stable@vger.kernel.org> # v4.16
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>

fs/overlayfs/export.c

@@ -257,7 +257,7 @@ static int ovl_encode_fh(struct inode *inode, u32 *fid, int *max_len,
 		return FILEID_INVALID;
 
 	dentry = d_find_any_alias(inode);
-	if (WARN_ON(!dentry))
+	if (!dentry)
 		return FILEID_INVALID;
 
 	bytes = ovl_dentry_to_fid(dentry, fid, buflen);