Re: [syzbot] task hung in exfat_write_inode

[syzbot]

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Subject: task hung in exfat_write_inode
Author: lizhi.xu@xxxxxxxxxxxxx

#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..4bdcdf126a21 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -132,14 +132,18 @@ int __exfat_truncate(struct inode *inode)
 			clu.dir += num_clusters;
 			clu.size -= num_clusters;
 		} else {
+			mutex_unlock(&sbi->s_lock);
 			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--;
 			}
+			mutex_lock(&sbi->s_lock);
 		}
 	} else {
 		ei->flags = ALLOC_NO_FAT_CHAIN;