jbd2: fix race between jbd2_journal_remove_checkpoint and ->j_commit_callback

commit 794446c6946513c684d448205fbd76fa35f38b72 upstream.

The following race is possible:

[kjournald2]                              other_task
jbd2_journal_commit_transaction()
  j_state = T_FINISHED;
  spin_unlock(&journal->j_list_lock);
                                         ->jbd2_journal_remove_checkpoint()
					   ->jbd2_journal_free_transaction();
					     ->kmem_cache_free(transaction)
  ->j_commit_callback(journal, transaction);
    -> USE_AFTER_FREE

WARNING: at lib/list_debug.c:62 __list_del_entry+0x1c0/0x250()
Hardware name:
list_del corruption. prev->next should be ffff88019a4ec198, but was 6b6b6b6b6b6b6b6b
Modules linked in: cpufreq_ondemand acpi_cpufreq freq_table mperf coretemp kvm_intel kvm crc32c_intel ghash_clmulni_intel microcode sg xhci_hcd button sd_mod crc_t10dif aesni_intel ablk_helper cryptd lrw aes_x86_64 xts gf128mul ahci libahci pata_acpi ata_generic dm_mirror dm_region_hash dm_log dm_mod
Pid: 16400, comm: jbd2/dm-1-8 Tainted: G        W    3.8.0-rc3+ #107
Call Trace:
 [<ffffffff8106fb0d>] warn_slowpath_common+0xad/0xf0
 [<ffffffff8106fc06>] warn_slowpath_fmt+0x46/0x50
 [<ffffffff813637e9>] ? ext4_journal_commit_callback+0x99/0xc0
 [<ffffffff8148cae0>] __list_del_entry+0x1c0/0x250
 [<ffffffff813637bf>] ext4_journal_commit_callback+0x6f/0xc0
 [<ffffffff813ca336>] jbd2_journal_commit_transaction+0x23a6/0x2570
 [<ffffffff8108aa42>] ? try_to_del_timer_sync+0x82/0xa0
 [<ffffffff8108b491>] ? del_timer_sync+0x91/0x1e0
 [<ffffffff813d3ecf>] kjournald2+0x19f/0x6a0
 [<ffffffff810ad630>] ? wake_up_bit+0x40/0x40
 [<ffffffff813d3d30>] ? bit_spin_lock+0x80/0x80
 [<ffffffff810ac6be>] kthread+0x10e/0x120
 [<ffffffff810ac5b0>] ? __init_kthread_worker+0x70/0x70
 [<ffffffff818ff6ac>] ret_from_fork+0x7c/0xb0
 [<ffffffff810ac5b0>] ? __init_kthread_worker+0x70/0x70

In order to demonstrace this issue one should mount ext4 with mount -o
discard option on SSD disk.  This makes callback longer and race
window becomes wider.

In order to fix this we should mark transaction as finished only after
callbacks have completed

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
[bwh: Backported to 3.2: s/jbd2_journal_free_transaction/kfree/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index d751f04763c1b740d7aa6b53f9a725027b01a1d9..ab9463a1947ec08e25b4a95d3ed4709634edcf2b 100644 (file)
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -326,7 +326,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
        int space_left = 0;
        int first_tag = 0;
        int tag_flag;
-       int i, to_free = 0;
+       int i;
        int tag_bytes = journal_tag_bytes(journal);
        struct buffer_head *cbh = NULL; /* For transactional checksums */
        __u32 crc32_sum = ~0;
@@ -996,7 +996,7 @@ restart_loop:
        journal->j_stats.run.rs_blocks_logged += stats.run.rs_blocks_logged;
        spin_unlock(&journal->j_history_lock);
 
-       commit_transaction->t_state = T_FINISHED;
+       commit_transaction->t_state = T_COMMIT_CALLBACK;
        J_ASSERT(commit_transaction == journal->j_committing_transaction);
        journal->j_commit_sequence = commit_transaction->t_tid;
        journal->j_committing_transaction = NULL;
@@ -1011,38 +1011,44 @@ restart_loop:
                                journal->j_average_commit_time*3) / 4;
        else
                journal->j_average_commit_time = commit_time;
+
        write_unlock(&journal->j_state_lock);
 
-       if (commit_transaction->t_checkpoint_list == NULL &&
-           commit_transaction->t_checkpoint_io_list == NULL) {
-               __jbd2_journal_drop_transaction(journal, commit_transaction);
-               to_free = 1;
+       if (journal->j_checkpoint_transactions == NULL) {
+               journal->j_checkpoint_transactions = commit_transaction;
+               commit_transaction->t_cpnext = commit_transaction;
+               commit_transaction->t_cpprev = commit_transaction;
        } else {
-               if (journal->j_checkpoint_transactions == NULL) {
-                       journal->j_checkpoint_transactions = commit_transaction;
-                       commit_transaction->t_cpnext = commit_transaction;
-                       commit_transaction->t_cpprev = commit_transaction;
-               } else {
-                       commit_transaction->t_cpnext =
-                               journal->j_checkpoint_transactions;
-                       commit_transaction->t_cpprev =
-                               commit_transaction->t_cpnext->t_cpprev;
-                       commit_transaction->t_cpnext->t_cpprev =
-                               commit_transaction;
-                       commit_transaction->t_cpprev->t_cpnext =
+               commit_transaction->t_cpnext =
+                       journal->j_checkpoint_transactions;
+               commit_transaction->t_cpprev =
+                       commit_transaction->t_cpnext->t_cpprev;
+               commit_transaction->t_cpnext->t_cpprev =
+                       commit_transaction;
+               commit_transaction->t_cpprev->t_cpnext =
                                commit_transaction;
-               }
        }
        spin_unlock(&journal->j_list_lock);
-
+       /* Drop all spin_locks because commit_callback may be block.
+        * __journal_remove_checkpoint() can not destroy transaction
+        * under us because it is not marked as T_FINISHED yet */
        if (journal->j_commit_callback)
                journal->j_commit_callback(journal, commit_transaction);
 
        trace_jbd2_end_commit(journal, commit_transaction);
        jbd_debug(1, "JBD2: commit %d complete, head %d\n",
                  journal->j_commit_sequence, journal->j_tail_sequence);
-       if (to_free)
-               kfree(commit_transaction);
 
+       write_lock(&journal->j_state_lock);
+       spin_lock(&journal->j_list_lock);
+       commit_transaction->t_state = T_FINISHED;
+       /* Recheck checkpoint lists after j_list_lock was dropped */
+       if (commit_transaction->t_checkpoint_list == NULL &&
+           commit_transaction->t_checkpoint_io_list == NULL) {
+               __jbd2_journal_drop_transaction(journal, commit_transaction);
+               kfree(commit_transaction);
+       }
+       spin_unlock(&journal->j_list_lock);
+       write_unlock(&journal->j_state_lock);
        wake_up(&journal->j_wait_done_commit);
 }

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index d1fd06396f354d19c9281aecac6d6a593d6435b4..a153ed52e64f8a558c4f7454f533909bf492f085 100644 (file)
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -470,6 +470,7 @@ struct transaction_s
                T_COMMIT,
                T_COMMIT_DFLUSH,
                T_COMMIT_JFLUSH,
+               T_COMMIT_CALLBACK,
                T_FINISHED
        }                       t_state;