On 07/14/2010 02:05 PM, Josef Bacik wrote: > On Wed, Jul 14, 2010 at 01:58:46PM -0500, Brian King wrote: >> >> I've been debugging a hang in jbd2_journal_release_jbd_inode >> which is being seen on Power 6 systems quite a lot. When we get >> in the hung state, all I/O to the disk in question gets blocked >> where we stay indefinitely. Looking at the task list, I can see >> we are stuck in jbd2_journal_release_jbd_inode waiting on a >> wake up. I added some debug code to detect this scenario and >> dump additional data if we were stuck in jbd2_journal_release_jbd_inode >> for longer than 30 minutes. When it hit, I was able to see that >> i_flags was 0, suggesting we missed the wake up. >> >> This patch changes i_flags to be an unsigned long, uses bit operators >> to access it, and adds barriers around the accesses. Prior to applying >> this patch, we were regularly hitting this hang on numerous systems >> in our test environment. After applying the patch, the hangs no longer >> occur. Its still not clear to me why the j_list_lock doesn't protect us >> in this path. It also appears a hang very similar to this was seen >> in the past and then was no longer recreatable: >> >> http://forum.soft32.com/linux/20090310-ext4-hangs-ftopict478916.html >> >> Signed-off-by: Brian King <brking@xxxxxxxxxxxxxxxxxx> >> --- >> >> fs/jbd2/commit.c | 12 ++++++++---- >> fs/jbd2/journal.c | 5 ++++- >> include/linux/jbd2.h | 2 +- >> 3 files changed, 13 insertions(+), 6 deletions(-) >> >> diff -puN include/linux/jbd2.h~jbd2_ji_commit_barrier_patch include/linux/jbd2.h >> --- linux-2.6/include/linux/jbd2.h~jbd2_ji_commit_barrier_patch 2010-07-14 13:46:17.000000000 -0500 >> +++ linux-2.6-bjking1/include/linux/jbd2.h 2010-07-14 13:46:17.000000000 -0500 >> @@ -395,7 +395,7 @@ struct jbd2_inode { >> struct inode *i_vfs_inode; >> >> /* Flags of inode [j_list_lock] */ >> - unsigned int i_flags; >> + unsigned long i_flags; >> }; >> >> struct jbd2_revoke_table_s; >> diff -puN fs/jbd2/commit.c~jbd2_ji_commit_barrier_patch fs/jbd2/commit.c >> --- linux-2.6/fs/jbd2/commit.c~jbd2_ji_commit_barrier_patch 2010-07-14 13:46:17.000000000 -0500 >> +++ linux-2.6-bjking1/fs/jbd2/commit.c 2010-07-14 13:56:27.000000000 -0500 >> @@ -26,7 +26,9 @@ >> #include <linux/backing-dev.h> >> #include <linux/bio.h> >> #include <linux/blkdev.h> >> +#include <linux/bitops.h> >> #include <trace/events/jbd2.h> >> +#include <asm/system.h> >> >> /* >> * Default IO end handler for temporary BJ_IO buffer_heads. >> @@ -245,7 +247,7 @@ static int journal_submit_data_buffers(j >> spin_lock(&journal->j_list_lock); >> list_for_each_entry(jinode, &commit_transaction->t_inode_list, i_list) { >> mapping = jinode->i_vfs_inode->i_mapping; >> - jinode->i_flags |= JI_COMMIT_RUNNING; >> + set_bit(__JI_COMMIT_RUNNING, &jinode->i_flags); >> spin_unlock(&journal->j_list_lock); >> /* >> * submit the inode data buffers. We use writepage >> @@ -260,7 +262,8 @@ static int journal_submit_data_buffers(j >> spin_lock(&journal->j_list_lock); >> J_ASSERT(jinode->i_transaction == commit_transaction); >> commit_transaction->t_flushed_data_blocks = 1; >> - jinode->i_flags &= ~JI_COMMIT_RUNNING; >> + clear_bit(__JI_COMMIT_RUNNING, &jinode->i_flags); >> + smp_mb__after_clear_bit(); >> wake_up_bit(&jinode->i_flags, __JI_COMMIT_RUNNING); >> } >> spin_unlock(&journal->j_list_lock); >> @@ -281,7 +284,7 @@ static int journal_finish_inode_data_buf >> /* For locking, see the comment in journal_submit_data_buffers() */ >> spin_lock(&journal->j_list_lock); >> list_for_each_entry(jinode, &commit_transaction->t_inode_list, i_list) { >> - jinode->i_flags |= JI_COMMIT_RUNNING; >> + set_bit(__JI_COMMIT_RUNNING, &jinode->i_flags); >> spin_unlock(&journal->j_list_lock); >> err = filemap_fdatawait(jinode->i_vfs_inode->i_mapping); >> if (err) { >> @@ -297,7 +300,8 @@ static int journal_finish_inode_data_buf >> ret = err; >> } >> spin_lock(&journal->j_list_lock); >> - jinode->i_flags &= ~JI_COMMIT_RUNNING; >> + clear_bit(__JI_COMMIT_RUNNING, &jinode->i_flags); >> + smp_mb__after_clear_bit(); >> wake_up_bit(&jinode->i_flags, __JI_COMMIT_RUNNING); >> } >> >> diff -puN fs/jbd2/journal.c~jbd2_ji_commit_barrier_patch fs/jbd2/journal.c >> --- linux-2.6/fs/jbd2/journal.c~jbd2_ji_commit_barrier_patch 2010-07-14 13:46:17.000000000 -0500 >> +++ linux-2.6-bjking1/fs/jbd2/journal.c 2010-07-14 13:46:17.000000000 -0500 >> @@ -41,12 +41,14 @@ >> #include <linux/hash.h> >> #include <linux/log2.h> >> #include <linux/vmalloc.h> >> +#include <linux/bitops.h> >> >> #define CREATE_TRACE_POINTS >> #include <trace/events/jbd2.h> >> >> #include <asm/uaccess.h> >> #include <asm/page.h> >> +#include <asm/system.h> >> >> EXPORT_SYMBOL(jbd2_journal_start); >> EXPORT_SYMBOL(jbd2_journal_restart); >> @@ -2209,9 +2211,10 @@ void jbd2_journal_release_jbd_inode(jour >> restart: >> spin_lock(&journal->j_list_lock); >> /* Is commit writing out inode - we have to wait */ >> - if (jinode->i_flags & JI_COMMIT_RUNNING) { >> + if (test_bit(__JI_COMMIT_RUNNING, &jinode->i_flags)) { >> wait_queue_head_t *wq; >> DEFINE_WAIT_BIT(wait, &jinode->i_flags, __JI_COMMIT_RUNNING); >> + smp_mb(); >> wq = bit_waitqueue(&jinode->i_flags, __JI_COMMIT_RUNNING); >> prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE); >> spin_unlock(&journal->j_list_lock); >> _ > > Seems reasonable to me, I assume you re-tested with this patch to make sure it > still fixes the problem? You can add I'm building a kernel with the updated patch and we will load it up on the failing systems and retest. It usually takes a number of hours before the problem hits on our test systems, so I may have some early results tomorrow. Thanks, Brian -- Brian King Linux on Power Virtualization IBM Linux Technology Center -- 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
