Re: [syzbot] task hung in exfat_write_inode

[syzbot <syzbot+2f73ed585f115e98aee8@syzkaller.appspotmail.com>]

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Subject: task hung in exfat_write_inode
Author: lizhi.xu@windriver.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git f9ff5644bcc0

diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index bfdfafe00993..a3ace4fc555c 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -116,6 +116,7 @@ int __exfat_truncate(struct inode *inode)
 
 	exfat_chain_set(&clu, ei->start_clu, num_clusters_phys, ei->flags);
 
+	mutex_unlock(&sbi->s_lock);
 	if (i_size_read(inode) > 0) {
 		/*
 		 * Truncate FAT chain num_clusters after the first cluster
@@ -134,8 +135,10 @@ int __exfat_truncate(struct inode *inode)
 		} else {
 			while (num_clusters > 0) {
 				last_clu = clu.dir;
+				mutex_lock(&sbi->s_lock);
 				if (exfat_get_next_cluster(sb, &(clu.dir)))
 					return -EIO;
+				mutex_unlock(&sbi->s_lock);
 
 				num_clusters--;
 				clu.size--;
@@ -160,6 +163,7 @@ int __exfat_truncate(struct inode *inode)
 	 * __exfat_write_inode() is called for directory entry, bitmap
 	 * and FAT to be written in a same writeback.
 	 */
+	mutex_lock(&sbi->s_lock);
 	if (__exfat_write_inode(inode, inode_needs_sync(inode)))
 		return -EIO;