| Message ID | 49064027.9010509@redhat.com |
|---|---|
| State | Superseded, archived |
| Headers | show |
On Mon, Oct 27, 2008 at 05:26:47PM -0500, Eric Sandeen wrote: > Ted, you probably need some slab debugging on to hit it. I had slab debugging enabled, but haven't been able to replicate it yet. I'll do some more work to try to replicate it. > I think the problem is that jbd2_journal_commit_transaction may call > __jbd2_journal_drop_transaction(journal, commit_transaction) if the > checkpoint lists are NULL, and this frees the commit_transaction. I think you're right. I would probably change the patch around so that after calling __jbd2_jurnal_drop_transaction(), we set commit_transaction to NULL, and then adding an "if (commit_transaction)" to the lines in questions; that way we keep the commit callback outside of the j_list_lock() spinlock. > Also, I'm not certain that it matters, but the loop in > release_blocks_on_commit() is kfreeing list entries w/o taking > them off the list; I suppose maybe this is safe if the whole thing > is getting discarded when we're done, but just to keep things sane, > would this make sense There are plenty of other loops in the kernel where we go through the linked list and free all of the items on the list that don't bother to call list_del(). That was one of the things I checked when I created the patch. > (also, I think we need to double-check use of > s_md_lock; it's taken when adding things to the list, but not when > freeing/removing ... if it's needed, isn't it needed on both ends...): No, because the linked list is hanging off the transaction structure. While the transaction is active, multiple CPU's can be adding elements to the linked list. But once the transaction has been committed, we don't have to worry about any one else trying to modify the linked list. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Theodore Tso wrote: > On Mon, Oct 27, 2008 at 05:26:47PM -0500, Eric Sandeen wrote: >> Ted, you probably need some slab debugging on to hit it. > > I had slab debugging enabled, but haven't been able to replicate it > yet. I'll do some more work to try to replicate it. > >> I think the problem is that jbd2_journal_commit_transaction may call >> __jbd2_journal_drop_transaction(journal, commit_transaction) if the >> checkpoint lists are NULL, and this frees the commit_transaction. > > I think you're right. I would probably change the patch around so > that after calling __jbd2_jurnal_drop_transaction(), we set > commit_transaction to NULL, and then adding an "if > (commit_transaction)" to the lines in questions; that way we keep the > commit callback outside of the j_list_lock() spinlock. Ok, I thought about that; sounds good. will resend. >> Also, I'm not certain that it matters, but the loop in >> release_blocks_on_commit() is kfreeing list entries w/o taking >> them off the list; I suppose maybe this is safe if the whole thing >> is getting discarded when we're done, but just to keep things sane, >> would this make sense > > There are plenty of other loops in the kernel where we go through the > linked list and free all of the items on the list that don't bother to > call list_del(). That was one of the things I checked when I created > the patch. Ok. >> (also, I think we need to double-check use of >> s_md_lock; it's taken when adding things to the list, but not when >> freeing/removing ... if it's needed, isn't it needed on both ends...): > > No, because the linked list is hanging off the transaction structure. > While the transaction is active, multiple CPU's can be adding elements > to the linked list. But once the transaction has been committed, we > don't have to worry about any one else trying to modify the linked list. > > - Ted ok, just double checking. Thanks, -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Index: linux-2.6/fs/jbd2/commit.c =================================================================== --- linux-2.6.orig/fs/jbd2/commit.c 2008-10-27 11:24:42.000000000 -0500 +++ linux-2.6/fs/jbd2/commit.c 2008-10-27 17:19:22.771063324 -0500 @@ -992,15 +992,15 @@ restart_loop: commit_transaction->t_cpprev->t_cpnext = commit_transaction; } + if (journal->j_commit_callback) + journal->j_commit_callback(journal, commit_transaction); + + trace_mark(jbd2_end_commit, "dev %s transaction %d head %d", + journal->j_devname, commit_transaction->t_tid, + journal->j_tail_sequence); } spin_unlock(&journal->j_list_lock); - if (journal->j_commit_callback) - journal->j_commit_callback(journal, commit_transaction); - - trace_mark(jbd2_end_commit, "dev %s transaction %d head %d", - journal->j_devname, commit_transaction->t_tid, - journal->j_tail_sequence); jbd_debug(1, "JBD: commit %d complete, head %d\n", journal->j_commit_sequence, journal->j_tail_sequence); Also, I'm not certain that it matters, but the loop in release_blocks_on_commit() is kfreeing list entries w/o taking them off the list; I suppose maybe this is safe if the whole thing is getting discarded when we're done, but just to keep things sane, would this make sense (also, I think we need to double-check use of s_md_lock; it's taken when adding things to the list, but not when freeing/removing ... if it's needed, isn't it needed on both ends...): Index: linux-2.6/fs/ext4/mballoc.c =================================================================== --- linux-2.6.orig/fs/ext4/mballoc.c 2008-10-27 11:24:41.000000000 -0500 +++ linux-2.6/fs/ext4/mballoc.c 2008-10-27 17:19:43.401064490 -0500 @@ -2644,6 +2644,7 @@ static void release_blocks_on_commit(jou struct super_block *sb = journal->j_private; struct ext4_buddy e4b; struct ext4_group_info *db; + struct ext4_sb_info *sbi = EXT4_SB(sb); int err, count = 0, count2 = 0; struct ext4_free_data *entry; ext4_fsblk_t discard_block; @@ -2683,6 +2684,9 @@ static void release_blocks_on_commit(jou (unsigned long long) discard_block, entry->count); sb_issue_discard(sb, discard_block, entry->count); + spin_lock(&sbi->s_md_lock); + list_del(&entry->list); + spin_unlock(&sbi->s_md_lock); kmem_cache_free(ext4_free_ext_cachep, entry); ext4_mb_release_desc(&e4b); }