This checks during journal commit, right after calculating the
checksum of a buffer head, whether its contents match the 'BUG'
string (the cookie string in the test case userspace part.)
If so, it sleeps 5 seconds for such contents to change (i.e.,
so that the actual checksum changes from what was calculated.)
And if it changed, set a flag to panic after committing to disk.
Then, on filesystem remount/journal recovery there is an invalid
checksum error, and recovery fails:
$ sudo mount -o data=journal,journal_checksum $DEV $MNT
[ 100.832223] EXT4-fs: Warning: mounting with data=journal disables
delayed allocation, dioread_nolock, and O_DIRECT support!
[ 100.837488] JBD2: Invalid checksum recovering data block 8706 in log
[ 100.842010] JBD2: recovery failed
[ 100.843045] EXT4-fs (loop0): error loading journal
mount: /ext4: can't read superblock on /dev/loop0.
---
fs/jbd2/commit.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 6d2da8ad0e6f..51f713089e35 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -26,6 +26,11 @@
#include <linux/bitops.h>
#include <trace/events/jbd2.h>
+#include <linux/printk.h>
+#include <linux/delay.h>
+
+static journal_t *force_panic;
+
/*
* IO end handler for temporary buffer_heads handling writes to the journal.
*/
@@ -331,14 +336,35 @@ static void jbd2_block_tag_csum_set(journal_t *j, journal_block_tag_t *tag,
__u32 csum32;
__be32 seq;
+ // For the testcase
+ __u32 csum32_later;
+ __u8 *bh_data;
+
if (!jbd2_journal_has_csum_v2or3(j))
return;
seq = cpu_to_be32(sequence);
addr = kmap_atomic(page);
csum32 = jbd2_chksum(j, j->j_csum_seed, (__u8 *)&seq, sizeof(seq));
+ csum32_later = csum32; // Copy csum32 to check again later
csum32 = jbd2_chksum(j, csum32, addr + offset_in_page(bh->b_data),
bh->b_size);
+
+ // Check for testcase cookie 'BUG' in the buffer_head data.
+ bh_data = addr + offset_in_page(bh->b_data);
+ if (bh_data[0] == 'B' &&
+ bh_data[1] == 'U' &&
+ bh_data[2] == 'G') {
+ pr_info("TESTCASE: Cookie found. Waiting 5 seconds for changes.\n");
+ msleep(5000);
+ pr_info("TESTCASE: Cookie eaten. Resumed.\n");
+ }
+
+ // Check the checksum again for changes/panic after commit.
+ csum32_later = jbd2_chksum(j, csum32_later, addr + offset_in_page(bh->b_data), bh->b_size);
+ if (csum32 != csum32_later)
+ force_panic = j;
+
kunmap_atomic(addr);
if (jbd2_has_feature_csum3(j))
@@ -885,6 +911,9 @@ void jbd2_journal_commit_transaction(journal_t *journal)
blkdev_issue_flush(journal->j_dev, GFP_NOFS);
}
+ if (force_panic == journal)
+ panic("TESTCASE: checksum changed; commit record done; panic!\n");
+
if (err)
jbd2_journal_abort(journal, err);
--
2.17.1
