ext4: don't set dioread_nolock by default for blocksize < pagesize

Currently on calling echo 3 > drop_caches on host machine, we see
FS corruption in the guest. This happens on Power machine where
blocksize < pagesize.

So as a temporary workaound don't enable dioread_nolock by default
for blocksize < pagesize until we identify the root cause.

Also emit a warning msg in case if this mount option is manually
enabled for blocksize < pagesize.

Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/20200327200744.12473-1-riteshh@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4d460747cca7443edfa757cb58f695c94fa8d567..c5639c0ba2c5234a7222f2e40fc489215ca83c8f 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2187,6 +2187,14 @@ static int parse_options(char *options, struct super_block *sb,
                }
        }
 #endif
+       if (test_opt(sb, DIOREAD_NOLOCK)) {
+               int blocksize =
+                       BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
+               if (blocksize < PAGE_SIZE)
+                       ext4_msg(sb, KERN_WARNING, "Warning: mounting with an "
+                                "experimental mount option 'dioread_nolock' "
+                                "for blocksize < PAGE_SIZE");
+       }
        return 1;
 }
 
@@ -3793,7 +3801,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                set_opt(sb, NO_UID32);
        /* xattr user namespace & acls are now defaulted on */
        set_opt(sb, XATTR_USER);
-       set_opt(sb, DIOREAD_NOLOCK);
 #ifdef CONFIG_EXT4_FS_POSIX_ACL
        set_opt(sb, POSIX_ACL);
 #endif
@@ -3843,6 +3850,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
        sbi->s_li_wait_mult = EXT4_DEF_LI_WAIT_MULT;
 
        blocksize = BLOCK_SIZE << le32_to_cpu(es->s_log_block_size);
+
+       if (blocksize == PAGE_SIZE)
+               set_opt(sb, DIOREAD_NOLOCK);
+
        if (blocksize < EXT4_MIN_BLOCK_SIZE ||
            blocksize > EXT4_MAX_BLOCK_SIZE) {
                ext4_msg(sb, KERN_ERR,