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And the following data-race was reported in my fuzzer: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D BUG: KCSAN: data-race in jbd2_journal_dirty_metadata / jbd2_journal_dirty_m= etadata write to 0xffff888011024104 of 4 bytes by task 10881 on cpu 1: jbd2_journal_dirty_metadata+0x2a5/0x770 fs/jbd2/transaction.c:1556 __ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358 ext4_do_update_inode fs/ext4/inode.c:5220 [inline] ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869 __ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074 ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103 .... read to 0xffff888011024104 of 4 bytes by task 10880 on cpu 0: jbd2_journal_dirty_metadata+0xf2/0x770 fs/jbd2/transaction.c:1512 __ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358 ext4_do_update_inode fs/ext4/inode.c:5220 [inline] ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869 __ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074 ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103 .... value changed: 0x00000000 -> 0x00000001 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D According to this crash report, there is a read/write data-race in jh->b_modified. This is because the b_state_lock is locked too late. For some reason, jbd2_journal_dirty_metadata() has been written in a way that it does not lock b_state_lock before checking jh->b_transaction. However, This makes the code that checks jh->b_transaction messy and causes a data-race in jh->b_* variables. Since locking b_state_lock earlier is not enough to significantly affect performance and most of the functions defined in transaction.c lock b_state_lock before reading/writing jh->b_*. Thereforce, I think it would be appropriate to modify=20 jbd2_journal_dirty_metadata() to lock b_state_lock earlier as well. Reported-by: syzbot+de24c3fe3c4091051710@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3Dde24c3fe3c4091051710 Fixes: 6e06ae88edae ("jbd2: speedup jbd2_journal_dirty_metadata()") Signed-off-by: Jeongjun Park --- fs/jbd2/transaction.c | 49 +++++++++++++++---------------------------- 1 file changed, 17 insertions(+), 32 deletions(-) diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index cbc4785462f5..7e6dbf37396f 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -1496,41 +1496,25 @@ int jbd2_journal_dirty_metadata(handle_t *handle, s= truct buffer_head *bh) jbd2_debug(5, "journal_head %p\n", jh); JBUFFER_TRACE(jh, "entry"); =20 - /* - * This and the following assertions are unreliable since we may see jh - * in inconsistent state unless we grab bh_state lock. But this is - * crucial to catch bugs so let's do a reliable check until the - * lockless handling is fully proven. - */ - if (data_race(jh->b_transaction !=3D transaction && - jh->b_next_transaction !=3D transaction)) { - spin_lock(&jh->b_state_lock); - J_ASSERT_JH(jh, jh->b_transaction =3D=3D transaction || - jh->b_next_transaction =3D=3D transaction); - spin_unlock(&jh->b_state_lock); - } + spin_lock(&jh->b_state_lock); + + J_ASSERT_JH(jh, jh->b_transaction =3D=3D transaction || + jh->b_next_transaction =3D=3D transaction); + if (jh->b_modified =3D=3D 1) { /* If it's in our transaction it must be in BJ_Metadata list. */ - if (data_race(jh->b_transaction =3D=3D transaction && - jh->b_jlist !=3D BJ_Metadata)) { - spin_lock(&jh->b_state_lock); - if (jh->b_transaction =3D=3D transaction && - jh->b_jlist !=3D BJ_Metadata) - pr_err("JBD2: assertion failure: h_type=3D%u " - "h_line_no=3D%u block_no=3D%llu jlist=3D%u\n", - handle->h_type, handle->h_line_no, - (unsigned long long) bh->b_blocknr, - jh->b_jlist); - J_ASSERT_JH(jh, jh->b_transaction !=3D transaction || - jh->b_jlist =3D=3D BJ_Metadata); - spin_unlock(&jh->b_state_lock); - } - goto out; + if (jh->b_transaction =3D=3D transaction && + jh->b_jlist !=3D BJ_Metadata) + pr_err("JBD2: assertion failure: h_type=3D%u " + "h_line_no=3D%u block_no=3D%llu jlist=3D%u\n", + handle->h_type, handle->h_line_no, + (unsigned long long) bh->b_blocknr, + jh->b_jlist); + J_ASSERT_JH(jh, jh->b_transaction !=3D transaction || + jh->b_jlist =3D=3D BJ_Metadata); + goto out_unlock_bh; } =20 - journal =3D transaction->t_journal; - spin_lock(&jh->b_state_lock); - if (is_handle_aborted(handle)) { /* * Check journal aborting with @jh->b_state_lock locked, @@ -1543,6 +1527,8 @@ int jbd2_journal_dirty_metadata(handle_t *handle, str= uct buffer_head *bh) goto out_unlock_bh; } =20 + journal =3D transaction->t_journal; + if (jh->b_modified =3D=3D 0) { /* * This buffer's got modified and becoming part @@ -1628,7 +1614,6 @@ int jbd2_journal_dirty_metadata(handle_t *handle, str= uct buffer_head *bh) spin_unlock(&journal->j_list_lock); out_unlock_bh: spin_unlock(&jh->b_state_lock); -out: JBUFFER_TRACE(jh, "exit"); return ret; } --