The following deadlock may happen when doing reservation for metadata:
Task0 Flush thread Task1
start_transaction()
shrink_delalloc()
writeback_inodes_sb_nr()
wait for flush thread
end.
btrfs_writepages()
cow_file_range()
btrfs_commit_transaction
wait num_writer == 1
(wait Task0 end
transaction)
start_transaction()
wait trans commit
end
Task0 -> Flush thread -> Task1 -> Task0
Fix the above deadlock by doing reservation before the trans handle has
been joined into the transaction.
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
---
fs/btrfs/extent-tree.c | 25 +++++++++++++----------
fs/btrfs/transaction.c | 51 +++++++++++++++++++++++++++++++++--------------
2 files changed, 50 insertions(+), 26 deletions(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index b42efc2..eefa432 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3290,9 +3290,11 @@ again:
/*
* shrink metadata reservation for delalloc
+ *
+ * NOTE: This function can not run in the transaction context, or deadlock
+ * will happen.
*/
-static int shrink_delalloc(struct btrfs_trans_handle *trans,
- struct btrfs_root *root, u64 to_reclaim, int sync)
+static int shrink_delalloc(struct btrfs_root *root, u64 to_reclaim)
{
struct btrfs_block_rsv *block_rsv;
struct btrfs_space_info *space_info;
@@ -3338,9 +3340,6 @@ static int shrink_delalloc(struct btrfs_trans_handle
*trans,
if (reserved == 0 || reclaimed >= max_reclaim)
break;
- if (trans && trans->transaction->blocked)
- return -EAGAIN;
-
time_left = schedule_timeout_interruptible(1);
/* We were interrupted, exit */
@@ -3449,12 +3448,16 @@ again:
/*
* We do synchronous shrinking since we don''t actually unreserve
* metadata until after the IO is completed.
+ *
+ * shrink_delalloc() can not run in the transaction context.
*/
- ret = shrink_delalloc(trans, root, num_bytes, 1);
- if (ret > 0)
- return 0;
- else if (ret < 0)
- goto out;
+ if (!trans || !trans->transaction) {
+ ret = shrink_delalloc(root, num_bytes);
+ if (ret > 0)
+ return 0;
+ else if (ret < 0)
+ goto out;
+ }
/*
* So if we were overcommitted it''s possible that somebody else
flushed
@@ -3989,7 +3992,7 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode,
u64 num_bytes)
block_rsv_add_bytes(block_rsv, to_reserve, 1);
if (block_rsv->size > 512 * 1024 * 1024)
- shrink_delalloc(NULL, root, to_reserve, 0);
+ shrink_delalloc(root, to_reserve);
return 0;
}
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 2b3590b..173b15d 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -222,9 +222,31 @@ again:
if (!h)
return ERR_PTR(-ENOMEM);
+ h->transid = 0;
+ h->transaction = NULL;
+ h->blocks_used = 0;
+ h->bytes_reserved = 0;
+ h->delayed_ref_updates = 0;
+ h->use_count = 1;
+ h->block_rsv = NULL;
+ h->orig_rsv = NULL;
+
if (may_wait_transaction(root, type))
wait_current_trans(root);
+ if (num_items > 0) {
+ /*
+ * Now the handle has not been joined into the transaction,
+ * so btrfs will shrink metadata reservation for delalloc if
+ * there is no enough free space to reserve.
+ */
+ ret = btrfs_trans_reserve_metadata(h, root, num_items);
+ if (ret < 0 && ret != -EAGAIN) {
+ kmem_cache_free(btrfs_trans_handle_cachep, h);
+ return ERR_PTR(ret);
+ }
+ }
+
do {
ret = join_transaction(root, type == TRANS_JOIN_NOLOCK);
if (ret == -EBUSY)
@@ -232,6 +254,7 @@ again:
} while (ret == -EBUSY);
if (ret < 0) {
+ btrfs_trans_release_metadata(h, root);
kmem_cache_free(btrfs_trans_handle_cachep, h);
return ERR_PTR(ret);
}
@@ -240,12 +263,6 @@ again:
h->transid = cur_trans->transid;
h->transaction = cur_trans;
- h->blocks_used = 0;
- h->bytes_reserved = 0;
- h->delayed_ref_updates = 0;
- h->use_count = 1;
- h->block_rsv = NULL;
- h->orig_rsv = NULL;
smp_mb();
if (cur_trans->blocked && may_wait_transaction(root, type)) {
@@ -253,21 +270,25 @@ again:
goto again;
}
- if (num_items > 0) {
- ret = btrfs_trans_reserve_metadata(h, root, num_items);
- if (ret == -EAGAIN && !retries) {
+ /*
+ * Though we shrink metadata reservation for delalloc, we might still
+ * not get enough free space, so we will commit the transaction and try
+ * to reclaim the reservation.
+ *
+ * NOTE: In the transaction context, we won''t shrink metadata
+ * reservation for delalloc, or the deadlock will happen.
+ */
+ if (num_items > 0 && !h->bytes_reserved) {
+ if (!retries) {
retries++;
btrfs_commit_transaction(h, root);
goto again;
- } else if (ret == -EAGAIN) {
+ } else {
/*
- * We have already retried and got EAGAIN, so really we
- * don''t have space, so set ret to -ENOSPC.
+ * We have already retried, so really we don''t have
+ * space, so set ret to -ENOSPC.
*/
ret = -ENOSPC;
- }
-
- if (ret < 0) {
btrfs_end_transaction(h, root);
return ERR_PTR(ret);
}
--
1.7.4
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Josef Bacik
2011-Jun-15 13:44 UTC
Re: [PATCH 2/2] btrfs: fix deadlock when doing reservation
On 06/15/2011 06:47 AM, Miao Xie wrote:> The following deadlock may happen when doing reservation for metadata: > > Task0 Flush thread Task1 > start_transaction() > shrink_delalloc() > writeback_inodes_sb_nr() > wait for flush thread > end. > btrfs_writepages() > cow_file_range() > btrfs_commit_transaction > wait num_writer == 1 > (wait Task0 end > transaction) > start_transaction() > wait trans commit > end > > Task0 -> Flush thread -> Task1 -> Task0 > > Fix the above deadlock by doing reservation before the trans handle has > been joined into the transaction. > > Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>I''ve already taken care of this in [PATCH 1/2] Btrfs: do transaction space reservation before joining the transaction 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
Mitch Harder
2011-Jun-16 14:36 UTC
Re: [PATCH 2/2] btrfs: fix deadlock when doing reservation
2011/6/15 Josef Bacik <josef@redhat.com>:> On 06/15/2011 06:47 AM, Miao Xie wrote: >> The following deadlock may happen when doing reservation for metadata: >> >> Task0 Flush thread Task1 >> start_transaction() >> shrink_delalloc() >> writeback_inodes_sb_nr() >> wait for flush thread >> end. >> btrfs_writepages() >> cow_file_range() >> btrfs_commit_transaction >> wait num_writer == 1 >> (wait Task0 end >> transaction) >> start_transaction() >> wait trans commit >> end >> >> Task0 -> Flush thread -> Task1 -> Task0 >> >> Fix the above deadlock by doing reservation before the trans handle has >> been joined into the transaction. >> >> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> > > I''ve already taken care of this in > > [PATCH 1/2] Btrfs: do transaction space reservation before joining the > transaction > > Thanks, > > JosefI''ve been trying to run down an issue with btrfs freezing with the 3.0_rc btrfs patch set. I''ve found a test case that repeatably freezes up on my system, and have been surveying the patches on the list to see if the issue has already been resolved. I''ve been successful in addressing the deadlock by applying Miao Xie''s patches (I''ve tested with both "[1/2] btrfs: fix wrong reservation when doing delayed inode operations" and "[2/2] btrfs: fix deadlock when doing reservation"). I''ve only been partially successful in running my test case with Josef Bacik''s patches (the deadlock is cleared; however, now I''m running into a premature ENOSPC). When evaluating Josef''s patches, I''ve applied: Btrfs: account for space reservations properly V2 Btrfs: fix btrfs_update_reserved_bytes usage [1/2] Btrfs: do transaction space reservation before joining the transaction [2/2] Btrfs: serialize flushers in reserve_metadata_bytes My test kernels are 2.6.39.1 kernels merged with the for-linus branch of Chris'' Btrfs unstable kernel tree. If Miao Xie''s patch is not going to be adopted, I''d like to get a clearer idea of the specific patches that are being put forward to address this issue, and I''ll apply my test case against those patches. It''s possible that I''ve applied too many of Josef''s proposed patches from the Mailing List, so let me know if I need to go another direction. -- 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-Jun-16 14:52 UTC
Re: [PATCH 2/2] btrfs: fix deadlock when doing reservation
On 06/16/2011 10:36 AM, Mitch Harder wrote:> 2011/6/15 Josef Bacik <josef@redhat.com>: >> On 06/15/2011 06:47 AM, Miao Xie wrote: >>> The following deadlock may happen when doing reservation for metadata: >>> >>> Task0 Flush thread Task1 >>> start_transaction() >>> shrink_delalloc() >>> writeback_inodes_sb_nr() >>> wait for flush thread >>> end. >>> btrfs_writepages() >>> cow_file_range() >>> btrfs_commit_transaction >>> wait num_writer == 1 >>> (wait Task0 end >>> transaction) >>> start_transaction() >>> wait trans commit >>> end >>> >>> Task0 -> Flush thread -> Task1 -> Task0 >>> >>> Fix the above deadlock by doing reservation before the trans handle has >>> been joined into the transaction. >>> >>> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> >> >> I''ve already taken care of this in >> >> [PATCH 1/2] Btrfs: do transaction space reservation before joining the >> transaction >> >> Thanks, >> >> Josef > > I''ve been trying to run down an issue with btrfs freezing with the > 3.0_rc btrfs patch set. I''ve found a test case that repeatably > freezes up on my system, and have been surveying the patches on the > list to see if the issue has already been resolved. > > I''ve been successful in addressing the deadlock by applying Miao Xie''s > patches (I''ve tested with both "[1/2] btrfs: fix wrong reservation > when doing delayed inode operations" and "[2/2] btrfs: fix deadlock > when doing reservation"). > > I''ve only been partially successful in running my test case with Josef > Bacik''s patches (the deadlock is cleared; however, now I''m running > into a premature ENOSPC). > > When evaluating Josef''s patches, I''ve applied: > Btrfs: account for space reservations properly V2 > Btrfs: fix btrfs_update_reserved_bytes usage > [1/2] Btrfs: do transaction space reservation before joining the transaction > [2/2] Btrfs: serialize flushers in reserve_metadata_bytes >So drop those first 2, they are wrong and why they are giving you early enospc. The last two are what you want and should fix your deadlock. 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
Mitch Harder
2011-Jun-16 17:17 UTC
Re: [PATCH 2/2] btrfs: fix deadlock when doing reservation
On Thu, Jun 16, 2011 at 9:52 AM, Josef Bacik <josef@redhat.com> wrote:> On 06/16/2011 10:36 AM, Mitch Harder wrote: >> 2011/6/15 Josef Bacik <josef@redhat.com>: >>> On 06/15/2011 06:47 AM, Miao Xie wrote: >>>> The following deadlock may happen when doing reservation for metadata: >>>> >>>> Task0 Flush thread Task1 >>>> start_transaction() >>>> shrink_delalloc() >>>> writeback_inodes_sb_nr() >>>> wait for flush thread >>>> end. >>>> btrfs_writepages() >>>> cow_file_range() >>>> btrfs_commit_transaction >>>> wait num_writer == 1 >>>> (wait Task0 end >>>> transaction) >>>> start_transaction() >>>> wait trans commit >>>> end >>>> >>>> Task0 -> Flush thread -> Task1 -> Task0 >>>> >>>> Fix the above deadlock by doing reservation before the trans handle has >>>> been joined into the transaction. >>>> >>>> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> >>> >>> I''ve already taken care of this in >>> >>> [PATCH 1/2] Btrfs: do transaction space reservation before joining the >>> transaction >>> >>> Thanks, >>> >>> Josef >> >> I''ve been trying to run down an issue with btrfs freezing with the >> 3.0_rc btrfs patch set. I''ve found a test case that repeatably >> freezes up on my system, and have been surveying the patches on the >> list to see if the issue has already been resolved. >> >> I''ve been successful in addressing the deadlock by applying Miao Xie''s >> patches (I''ve tested with both "[1/2] btrfs: fix wrong reservation >> when doing delayed inode operations" and "[2/2] btrfs: fix deadlock >> when doing reservation"). >> >> I''ve only been partially successful in running my test case with Josef >> Bacik''s patches (the deadlock is cleared; however, now I''m running >> into a premature ENOSPC). >> >> When evaluating Josef''s patches, I''ve applied: >> Btrfs: account for space reservations properly V2 >> Btrfs: fix btrfs_update_reserved_bytes usage >> [1/2] Btrfs: do transaction space reservation before joining the transaction >> [2/2] Btrfs: serialize flushers in reserve_metadata_bytes >> > > So drop those first 2, they are wrong and why they are giving you early > enospc. The last two are what you want and should fix your deadlock. > Thanks, >Confirmed. The deadlock is cleared in my test case when applying just the "[1/2] Btrfs: do transaction space reservation before joining the transaction" patch and the "[2/2] Btrfs: serialize flushers in reserve_metadata_bytes" patch. -- 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-Jun-16 17:17 UTC
Re: [PATCH 2/2] btrfs: fix deadlock when doing reservation
On 06/16/2011 01:17 PM, Mitch Harder wrote:> On Thu, Jun 16, 2011 at 9:52 AM, Josef Bacik <josef@redhat.com> wrote: >> On 06/16/2011 10:36 AM, Mitch Harder wrote: >>> 2011/6/15 Josef Bacik <josef@redhat.com>: >>>> On 06/15/2011 06:47 AM, Miao Xie wrote: >>>>> The following deadlock may happen when doing reservation for metadata: >>>>> >>>>> Task0 Flush thread Task1 >>>>> start_transaction() >>>>> shrink_delalloc() >>>>> writeback_inodes_sb_nr() >>>>> wait for flush thread >>>>> end. >>>>> btrfs_writepages() >>>>> cow_file_range() >>>>> btrfs_commit_transaction >>>>> wait num_writer == 1 >>>>> (wait Task0 end >>>>> transaction) >>>>> start_transaction() >>>>> wait trans commit >>>>> end >>>>> >>>>> Task0 -> Flush thread -> Task1 -> Task0 >>>>> >>>>> Fix the above deadlock by doing reservation before the trans handle has >>>>> been joined into the transaction. >>>>> >>>>> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> >>>> >>>> I''ve already taken care of this in >>>> >>>> [PATCH 1/2] Btrfs: do transaction space reservation before joining the >>>> transaction >>>> >>>> Thanks, >>>> >>>> Josef >>> >>> I''ve been trying to run down an issue with btrfs freezing with the >>> 3.0_rc btrfs patch set. I''ve found a test case that repeatably >>> freezes up on my system, and have been surveying the patches on the >>> list to see if the issue has already been resolved. >>> >>> I''ve been successful in addressing the deadlock by applying Miao Xie''s >>> patches (I''ve tested with both "[1/2] btrfs: fix wrong reservation >>> when doing delayed inode operations" and "[2/2] btrfs: fix deadlock >>> when doing reservation"). >>> >>> I''ve only been partially successful in running my test case with Josef >>> Bacik''s patches (the deadlock is cleared; however, now I''m running >>> into a premature ENOSPC). >>> >>> When evaluating Josef''s patches, I''ve applied: >>> Btrfs: account for space reservations properly V2 >>> Btrfs: fix btrfs_update_reserved_bytes usage >>> [1/2] Btrfs: do transaction space reservation before joining the transaction >>> [2/2] Btrfs: serialize flushers in reserve_metadata_bytes >>> >> >> So drop those first 2, they are wrong and why they are giving you early >> enospc. The last two are what you want and should fix your deadlock. >> Thanks, >> > > Confirmed. > > The deadlock is cleared in my test case when applying just the "[1/2] > Btrfs: do transaction space reservation before joining the > transaction" patch and the "[2/2] Btrfs: serialize flushers in > reserve_metadata_bytes" patch.Perfect, 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