Hi Ted:
Unfortunately, some deref in your printk didn't go over too well:
[ 970.871166] BUG: unable to handle kernel NULL pointer dereference
at 0000000000000008
[ 970.872139] IP: [<ffffffff812a158e>] jbd2_journal_dirty_metadata+0x18e/0x220
[ 970.872139] PGD 857b8d067 PUD 852f26067 PMD 0
[ 970.872139] Oops: 0000 [#1] SMP
[ 970.872139] CPU 14
...
[ 970.872139] Call Trace:
[ 970.872139] [<ffffffff812a9d26>] ? jbd2_journal_add_journal_head+0x86/0x290
[ 970.872139] [<ffffffff8125c87c>] ? __ext4_journalled_writepage+0xac/0x390
[ 970.872139] [<ffffffff812848b3>] __ext4_handle_dirty_metadata+0x83/0x120
[ 970.872139] [<ffffffff81284c1e>] ? __ext4_journal_get_write_access+0x3e/0x80
[ 970.872139] [<ffffffff8125cac8>] __ext4_journalled_writepage+0x2f8/0x390
[ 970.872139] [<ffffffff8125e264>] ext4_writepage+0x234/0x2f0
[ 970.872139] [<ffffffff81155ad7>] __writepage+0x17/0x40
...
where the IP corresponds to:
(gdb) list *0xffffffff812a158e
0xffffffff812a158e is in jbd2_journal_dirty_metadata
(fs/jbd2/transaction.c:1124).
1119 */
1120 if (jh->b_transaction != transaction) {
1121 JBUFFER_TRACE(jh, "already on other transaction");
1122 if (unlikely(jh->b_transaction !=
1123 journal->j_committing_transaction)) {
1124 printk(KERN_EMERG "JBD: %s: "
1125 "jh->b_transaction (%llu, %p, %u) != "
1126
"journal->j_committing_transaction (%p, %u)",
1127 journal->j_devname,
1128 (unsigned long long) bh->b_blocknr,
It seems that jh->b_transaction is NULL, and deferencing it to print
out jh->b_transaction->t_tid causes the NULL pointer deref.
Curt
On Sat, Aug 13, 2011 at 7:53 PM, Theodore Ts'o <tytso@xxxxxxx> wrote:
> These assertions have been reported as being tripped. Instrument them
> so we get more information about what might be going on.
>
> Cc: curtw@xxxxxxxxxx
> Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> ---
>
> Curt, you might want to see if you can replicate that jbd2 crash with
> this patch applied. Hopefully we'll get more information about what is
> going on.
>
> fs/jbd2/transaction.c | 42 +++++++++++++++++++++++++++++++++++++-----
> 1 files changed, 37 insertions(+), 5 deletions(-)
>
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index 2d71094..693fe63 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -1093,8 +1093,19 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
> */
> if (jh->b_transaction == transaction && jh->b_jlist == BJ_Metadata) {
> JBUFFER_TRACE(jh, "fastpath");
> - J_ASSERT_JH(jh, jh->b_transaction ==
> - journal->j_running_transaction);
> + if (unlikely(jh->b_transaction !=
> + journal->j_running_transaction)) {
> + printk(KERN_EMERG "JBD: %s: "
> + "jh->b_transaction (%llu, %p, %u) != "
> + "journal->j_running_transaction (%p, %u)",
> + journal->j_devname,
> + (unsigned long long) bh->b_blocknr,
> + jh->b_transaction,
> + jh->b_transaction->t_tid,
> + journal->j_running_transaction,
> + journal->j_running_transaction->t_tid);
> + BUG_ON(1);
> + }
> goto out_unlock_bh;
> }
>
> @@ -1108,9 +1119,30 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
> */
> if (jh->b_transaction != transaction) {
> JBUFFER_TRACE(jh, "already on other transaction");
> - J_ASSERT_JH(jh, jh->b_transaction ==
> - journal->j_committing_transaction);
> - J_ASSERT_JH(jh, jh->b_next_transaction == transaction);
> + if (unlikely(jh->b_transaction !=
> + journal->j_committing_transaction)) {
> + printk(KERN_EMERG "JBD: %s: "
> + "jh->b_transaction (%llu, %p, %u) != "
> + "journal->j_committing_transaction (%p, %u)",
> + journal->j_devname,
> + (unsigned long long) bh->b_blocknr,
> + jh->b_transaction,
> + jh->b_transaction->t_tid,
> + journal->j_committing_transaction,
> + journal->j_committing_transaction->t_tid);
> + BUG_ON(1);
> + }
> + if (unlikely(jh->b_next_transaction != transaction)) {
> + printk(KERN_EMERG "JBD: %s: "
> + "jh->b_next_transaction (%llu, %p, %u) != "
> + "transaction (%p, %u)",
> + journal->j_devname,
> + (unsigned long long) bh->b_blocknr,
> + jh->b_next_transaction,
> + jh->b_next_transaction->t_tid,
> + transaction, transaction->t_tid);
> + BUG_ON(1);
> + }
> /* And this case is illegal: we can't reuse another
> * transaction's data buffer, ever. */
> goto out_unlock_bh;
> --
> 1.7.4.1.22.gec8e1.dirty
>
>
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