* Eric Whitney <[email protected]>: > * Theodore Ts'o <[email protected]>: > > The commit cf108bca465d: "ext4: Invert the locking order of page_lock > > and transaction start" caused __ext4_journalled_writepage() to drop > > the page lock before the page was written back, as part of changing > > the locking order to jbd2_journal_start -> page_lock. However, this > > introduced a potential race if there was a truncate racing with the > > data=journalled writeback mode. > > > > Fix this by grabbing the page lock after starting the journal handle, > > and then checking to see if page had gotten truncated out from under > > us. > > > > This fixes a number of different crashes or BUG_ON's when running > > xfstests generic/086 in data=journalled mode, including: > > > > jbd2_journal_dirty_metadata: vdc-8: bad jh for block 84434: transaction > > (ec90434 > > ransaction ( (null), 0), jh->b_next_transaction ( (null), 0), jlist 0 > > > > - and - > > > > kernel BUG at /usr/projects/linux/ext4/fs/jbd2/transaction.c:2200! > > ... > > Call Trace: > > [<c02b2ded>] ? __ext4_journalled_invalidatepage+0x117/0x117 > > [<c02b2de5>] __ext4_journalled_invalidatepage+0x10f/0x117 > > [<c02b2ded>] ? __ext4_journalled_invalidatepage+0x117/0x117 > > [<c027d883>] ? lock_buffer+0x36/0x36 > > [<c02b2dfa>] ext4_journalled_invalidatepage+0xd/0x22 > > [<c0229139>] do_invalidatepage+0x22/0x26 > > [<c0229198>] truncate_inode_page+0x5b/0x85 > > [<c022934b>] truncate_inode_pages_range+0x156/0x38c > > [<c0229592>] truncate_inode_pages+0x11/0x15 > > [<c022962d>] truncate_pagecache+0x55/0x71 > > [<c02b913b>] ext4_setattr+0x4a9/0x560 > > [<c01ca542>] ? current_kernel_time+0x10/0x44 > > [<c026c4d8>] notify_change+0x1c7/0x2be > > [<c0256a00>] do_truncate+0x65/0x85 > > [<c0226f31>] ? file_ra_state_init+0x12/0x29 > > > > - and - > > > > WARNING: CPU: 1 PID: 1331 at > > /usr/projects/linux/ext4/fs/jbd2/transaction.c:1396 > > irty_metadata+0x14a/0x1ae() > > ... > > Call Trace: > > [<c01b879f>] ? console_unlock+0x3a1/0x3ce > > [<c082cbb4>] dump_stack+0x48/0x60 > > [<c0178b65>] warn_slowpath_common+0x89/0xa0 > > [<c02ef2cf>] ? jbd2_journal_dirty_metadata+0x14a/0x1ae > > [<c0178bef>] warn_slowpath_null+0x14/0x18 > > [<c02ef2cf>] jbd2_journal_dirty_metadata+0x14a/0x1ae > > [<c02d8615>] __ext4_handle_dirty_metadata+0xd4/0x19d > > [<c02b2f44>] write_end_fn+0x40/0x53 > > [<c02b4a16>] ext4_walk_page_buffers+0x4e/0x6a > > [<c02b59e7>] ext4_writepage+0x354/0x3b8 > > [<c02b2f04>] ? mpage_release_unused_pages+0xd4/0xd4 > > [<c02b1b21>] ? wait_on_buffer+0x2c/0x2c > > [<c02b5a4b>] ? ext4_writepage+0x3b8/0x3b8 > > [<c02b5a5b>] __writepage+0x10/0x2e > > [<c0225956>] write_cache_pages+0x22d/0x32c > > [<c02b5a4b>] ? ext4_writepage+0x3b8/0x3b8 > > [<c02b6ee8>] ext4_writepages+0x102/0x607 > > [<c019adfe>] ? sched_clock_local+0x10/0x10e > > [<c01a8a7c>] ? __lock_is_held+0x2e/0x44 > > [<c01a8ad5>] ? lock_is_held+0x43/0x51 > > [<c0226dff>] do_writepages+0x1c/0x29 > > [<c0276bed>] __writeback_single_inode+0xc3/0x545 > > [<c0277c07>] writeback_sb_inodes+0x21f/0x36d > > ... > > > > Signed-off-by: Theodore Ts'o <[email protected]> > > Cc: [email protected] > > --- > > fs/ext4/inode.c | 23 +++++++++++++++++++---- > > 1 file changed, 19 insertions(+), 4 deletions(-) > > > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > > index 0554b0b..263a46c 100644 > > --- a/fs/ext4/inode.c > > +++ b/fs/ext4/inode.c > > @@ -1701,19 +1701,32 @@ static int __ext4_journalled_writepage(struct page > > *page, > > ext4_walk_page_buffers(handle, page_bufs, 0, len, > > NULL, bget_one); > > } > > - /* As soon as we unlock the page, it can go away, but we have > > - * references to buffers so we are safe */ > > + /* > > + * We need to release the page lock before we start the > > + * journal, so grab a reference so the page won't disappear > > + * out from under us. > > + */ > > + get_page(page); > > unlock_page(page); > > > > handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, > > ext4_writepage_trans_blocks(inode)); > > if (IS_ERR(handle)) { > > ret = PTR_ERR(handle); > > - goto out; > > + put_page(page); > > + goto out_no_pagelock; > > } > > - > > BUG_ON(!ext4_handle_valid(handle)); > > > > + lock_page(page); > > + put_page(page); > > + if (page->mapping != mapping) { > > + /* The page got truncated from under us */ > > + ext4_journal_stop(handle); > > + ret = 0; > > + goto out; > > + } > > + > > if (inline_data) { > > BUFFER_TRACE(inode_bh, "get write access"); > > ret = ext4_journal_get_write_access(handle, inode_bh); > > @@ -1739,6 +1752,8 @@ static int __ext4_journalled_writepage(struct page > > *page, > > NULL, bput_one); > > ext4_set_inode_state(inode, EXT4_STATE_JDATA); > > out: > > + unlock_page(page); > > +out_no_pagelock: > > brelse(inode_bh); > > return ret; > > } > > -- > > 2.3.0 > > > > This patch looks promising. I'm running a 1000 trial stress test on a > Pandaboard where I've generally been able to force a couple of manifestations > of this bug to appear within 5 to 10 runs. Applied to 4.1-rc7, it's passed > 135 trials cleanly. The full series will complete sometime tomorrow. > > I was also able to reproduce the problem on x86_64 pretty consistently in > four runs or less on 4.1-rc7; I'm planning a stress test there as well once > -rc8 regression is complete. >
1000 consecutive runs of generic/068 on the data_journal test case have completed successfully on an x86_64 guest and a Pandaboard running a 4.1-rc7 kernel with this patch. That's a couple of orders of magnitude more runs than have previously completed without hangs on these test system configurations, so Tested-by: Eric Whitney <[email protected]> if useful at this point. Eric -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
