jbd2: fix off-by-one while erasing journal

In __jbd2_journal_erase(), the block_stop parameter includes the last
block of a contiguous region; however, the calculation of byte_stop is
incorrect, as it does not account for the bytes in that last block.
Consequently, the page cache is not cleared properly, which occasionally
causes the ext4/050 test to fail.

Since block_stop operates on inclusion semantics, it involves repeated
increments and decrements by 1, significantly increasing the complexity
of the calculations. Optimize the calculation and fix the incorrect
byte_stop by make both block_stop and byte_stop to use exclusion
semantics.

This fixes a failure in fstests ext4/050.

Fixes: 01d5d96 ("ext4: add discard/zeroout flags to journal flush")
Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: Baokun Li <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: zhangyi089

fs/jbd2/journal.c

@@ -1964,17 +1964,15 @@ static int __jbd2_journal_erase(journal_t *journal, unsigned int flags)
 			return err;
 		}
 
-		if (block_start == ~0ULL) {
-			block_start = phys_block;
-			block_stop = block_start - 1;
-		}
+		if (block_start == ~0ULL)
+			block_stop = block_start = phys_block;
 
 		/*
 		 * last block not contiguous with current block,
 		 * process last contiguous region and return to this block on
 		 * next loop
 		 */
-		if (phys_block != block_stop + 1) {
+		if (phys_block != block_stop) {
 			block--;
 		} else {
 			block_stop++;
@@ -1993,11 +1991,10 @@ static int __jbd2_journal_erase(journal_t *journal, unsigned int flags)
 		 */
 		byte_start = block_start * journal->j_blocksize;
 		byte_stop = block_stop * journal->j_blocksize;
-		byte_count = (block_stop - block_start + 1) *
-				journal->j_blocksize;
+		byte_count = (block_stop - block_start) * journal->j_blocksize;
 
 		truncate_inode_pages_range(journal->j_dev->bd_mapping,
-				byte_start, byte_stop);
+				byte_start, byte_stop - 1);
 
 		if (flags & JBD2_JOURNAL_FLUSH_DISCARD) {
 			err = blkdev_issue_discard(journal->j_dev,
@@ -2012,7 +2009,7 @@ static int __jbd2_journal_erase(journal_t *journal, unsigned int flags)
 		}
 
 		if (unlikely(err != 0)) {
-			pr_err("JBD2: (error %d) unable to wipe journal at physical blocks %llu - %llu",
+			pr_err("JBD2: (error %d) unable to wipe journal at physical blocks [%llu, %llu)",
 					err, block_start, block_stop);
 			return err;
 		}