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| author | Paul Gortmaker <paul.gortmaker@windriver.com> | 2013-06-12 22:47:35 -0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2013-06-12 22:47:35 -0400 |
| commit | 0ef54180e0187117062939202b96faf04c8673bc (patch) | |
| tree | 381e111981ae47b3862927d64cd6415ab308a43a /fs/jbd2/checkpoint.c | |
| parent | 3ca841c106fd6cd2c942985977a5d126434a8dd6 (diff) | |
| download | linux-0ef54180e0187117062939202b96faf04c8673bc.tar.gz | |
jbd2: drop checkpoint mutex when waiting in __jbd2_log_wait_for_space()
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@windriver.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to 'fs/jbd2/checkpoint.c')
| -rw-r--r-- | fs/jbd2/checkpoint.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c index 75a15f371b00..7f34f4716165 100644 --- a/fs/jbd2/checkpoint.c +++ b/fs/jbd2/checkpoint.c @@ -156,7 +156,15 @@ void __jbd2_log_wait_for_space(journal_t *journal) /* We were able to recover space; yay! */ ; } else if (tid) { + /* + * jbd2_journal_commit_transaction() may want + * to take the checkpoint_mutex if JBD2_FLUSHED + * is set. So we need to temporarily drop it. + */ + mutex_unlock(&journal->j_checkpoint_mutex); jbd2_log_wait_commit(journal, tid); + write_lock(&journal->j_state_lock); + continue; } else { printk(KERN_ERR "%s: needed %d blocks and " "only had %d space available\n", |