Josef Bacik
2011-Jul-14 17:26 UTC
[PATCH] Btrfs: fix deadlock when throttling transactions
Hit this nice little deadlock. What happens is this
__btrfs_end_transaction with throttle set, --use_count so it equals 0
btrfs_commit_transaction
<somebody else actually manages to start the commit>
btrfs_end_transaction --use_count so now its -1 <== BAD
we just return and wait on the transaction
This is bad because we just return after our use_count is -1 and don''t
let go
of our num_writer count on the transaction, so the guy committing the
transaction just sits there forever. Fix this by inc''ing our use_count
if we''re
going to call commit_transaction so that if we call btrfs_end_transaction
it''s
valid. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
---
fs/btrfs/transaction.c | 13 ++++++++++---
1 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 654755b..00b81fb5 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -497,10 +497,17 @@ static int __btrfs_end_transaction(struct
btrfs_trans_handle *trans,
}
if (lock && cur_trans->blocked && !cur_trans->in_commit)
{
- if (throttle)
+ if (throttle) {
+ /*
+ * We may race with somebody else here so end up having
+ * to call end_transaction on ourselves again, so inc
+ * our use_count.
+ */
+ trans->use_count++;
return btrfs_commit_transaction(trans, root);
- else
+ } else {
wake_up_process(info->transaction_kthread);
+ }
}
WARN_ON(cur_trans != info->running_transaction);
@@ -1225,7 +1232,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle
*trans,
if (cur_trans->in_commit) {
spin_unlock(&cur_trans->commit_lock);
atomic_inc(&cur_trans->use_count);
- btrfs_end_transaction(trans, root);
+ __btrfs_end_transaction(trans, root, 0, 1);
ret = wait_for_commit(root, cur_trans);
BUG_ON(ret);
--
1.7.5.2
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On 07/15/2011 01:26 AM, Josef Bacik wrote:> Hit this nice little deadlock. What happens is this > > __btrfs_end_transaction with throttle set, --use_count so it equals 0 > btrfs_commit_transaction > <somebody else actually manages to start the commit> > btrfs_end_transaction --use_count so now its -1 <== BAD > we just return and wait on the transaction > > This is bad because we just return after our use_count is -1 and don''t let go > of our num_writer count on the transaction, so the guy committing the > transaction just sits there forever. Fix this by inc''ing our use_count if we''re > going to call commit_transaction so that if we call btrfs_end_transaction it''s > valid. Thanks, > > Signed-off-by: Josef Bacik <josef@redhat.com> > --- > fs/btrfs/transaction.c | 13 ++++++++++--- > 1 files changed, 10 insertions(+), 3 deletions(-) > > diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c > index 654755b..00b81fb5 100644 > --- a/fs/btrfs/transaction.c > +++ b/fs/btrfs/transaction.c > @@ -497,10 +497,17 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans, > } > > if (lock && cur_trans->blocked && !cur_trans->in_commit) { > - if (throttle) > + if (throttle) { > + /* > + * We may race with somebody else here so end up having > + * to call end_transaction on ourselves again, so inc > + * our use_count. > + */ > + trans->use_count++; > return btrfs_commit_transaction(trans, root); > - else > + } else { > wake_up_process(info->transaction_kthread); > + } > } > > WARN_ON(cur_trans != info->running_transaction); > @@ -1225,7 +1232,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, > if (cur_trans->in_commit) { > spin_unlock(&cur_trans->commit_lock); > atomic_inc(&cur_trans->use_count); > - btrfs_end_transaction(trans, root); > + __btrfs_end_transaction(trans, root, 0, 1); >Looks good. BTW, btrfs_end_transaction(trans, root) is just __btrfs_end_transaction(trans, root, 0, 1). thanks, liubo> ret = wait_for_commit(root, cur_trans); > BUG_ON(ret);-- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Josef Bacik
2011-Jul-15 13:54 UTC
Re: [PATCH] Btrfs: fix deadlock when throttling transactions
On 07/14/2011 10:56 PM, liubo wrote:> On 07/15/2011 01:26 AM, Josef Bacik wrote: >> Hit this nice little deadlock. What happens is this >> >> __btrfs_end_transaction with throttle set, --use_count so it equals 0 >> btrfs_commit_transaction >> <somebody else actually manages to start the commit> >> btrfs_end_transaction --use_count so now its -1 <== BAD >> we just return and wait on the transaction >> >> This is bad because we just return after our use_count is -1 and don''t let go >> of our num_writer count on the transaction, so the guy committing the >> transaction just sits there forever. Fix this by inc''ing our use_count if we''re >> going to call commit_transaction so that if we call btrfs_end_transaction it''s >> valid. Thanks, >> >> Signed-off-by: Josef Bacik <josef@redhat.com> >> --- >> fs/btrfs/transaction.c | 13 ++++++++++--- >> 1 files changed, 10 insertions(+), 3 deletions(-) >> >> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c >> index 654755b..00b81fb5 100644 >> --- a/fs/btrfs/transaction.c >> +++ b/fs/btrfs/transaction.c >> @@ -497,10 +497,17 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans, >> } >> >> if (lock && cur_trans->blocked && !cur_trans->in_commit) { >> - if (throttle) >> + if (throttle) { >> + /* >> + * We may race with somebody else here so end up having >> + * to call end_transaction on ourselves again, so inc >> + * our use_count. >> + */ >> + trans->use_count++; >> return btrfs_commit_transaction(trans, root); >> - else >> + } else { >> wake_up_process(info->transaction_kthread); >> + } >> } >> >> WARN_ON(cur_trans != info->running_transaction); >> @@ -1225,7 +1232,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, >> if (cur_trans->in_commit) { >> spin_unlock(&cur_trans->commit_lock); >> atomic_inc(&cur_trans->use_count); >> - btrfs_end_transaction(trans, root); >> + __btrfs_end_transaction(trans, root, 0, 1); >> > > Looks good. > > BTW, btrfs_end_transaction(trans, root) is just __btrfs_end_transaction(trans, root, 0, 1). >Oops you''re right, I saw the 1 for lock and thought it was for throttle. Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html