On Tue, Jun 11, 2013 at 06:44:26PM -0400, Paul Gortmaker wrote: > While trying to debug an an issue under extreme I/O loading > on preempt-rt kernels, the following backtrace was observed > via SysRQ output: > > rm D ffff8802203afbc0 4600 4878 4748 0x00000000 > ffff8802217bfb78 0000000000000082 ffff88021fc2bb80 ffff88021fc2bb80 > ffff88021fc2bb80 ffff8802217bffd8 ffff8802217bffd8 ffff8802217bffd8 > ffff88021f1d4c80 ffff88021fc2bb80 ffff8802217bfb88 ffff88022437b000 > Call Trace: > [<ffffffff8172dc34>] schedule+0x24/0x70 > [<ffffffff81225b5d>] jbd2_log_wait_commit+0xbd/0x140 > [<ffffffff81060390>] ? __init_waitqueue_head+0x50/0x50 > [<ffffffff81223635>] jbd2_log_do_checkpoint+0xf5/0x520 > [<ffffffff81223b09>] __jbd2_log_wait_for_space+0xa9/0x1f0 > [<ffffffff8121dc40>] start_this_handle.isra.10+0x2e0/0x530 > [<ffffffff81060390>] ? __init_waitqueue_head+0x50/0x50 > [<ffffffff8121e0a3>] jbd2__journal_start+0xc3/0x110 > [<ffffffff811de7ce>] ? ext4_rmdir+0x6e/0x230 > [<ffffffff8121e0fe>] jbd2_journal_start+0xe/0x10 > [<ffffffff811f308b>] ext4_journal_start_sb+0x5b/0x160 > [<ffffffff811de7ce>] ext4_rmdir+0x6e/0x230 > [<ffffffff811435c5>] vfs_rmdir+0xd5/0x140 > [<ffffffff8114370f>] do_rmdir+0xdf/0x120 > [<ffffffff8105c6b4>] ? task_work_run+0x44/0x80 > [<ffffffff81002889>] ? do_notify_resume+0x89/0x100 > [<ffffffff817361ae>] ? int_signal+0x12/0x17 > [<ffffffff81145d85>] sys_unlinkat+0x25/0x40 > [<ffffffff81735f22>] system_call_fastpath+0x16/0x1b > > What is interesting here, is that we call log_wait_commit, from > within wait_for_space, but we are still holding the checkpoint_mutex > as it surrounds mostly the whole of wait_for_space. And then, as we > are waiting, journal_commit_transaction can run, and if the JBD2_FLUSHED > bit is set, then we will also try to take the same checkpoint_mutex. > > It seems that we need to drop the checkpoint_mutex while sitting in > jbd2_log_wait_commit, if we want to guarantee that progress can be made > by jbd2_journal_commit_transaction(). There does not seem to be > anything preempt-rt specific about this, other then perhaps increasing > the odds of it happening. > > Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx> Applied, thanks. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
