[Devel] [PATCH hci-8.1 v2 0/4] dm-ploop: fix the pio submission stop around cmds

[Devel] [PATCH hci-8.1 v2 0/4] dm-ploop: fix the pio submission stop around cmds

[Denis V. Lunev]

A cmd stops pio submission and waits for the inflight pios before it
rewrites the BAT levels or deltas[], and expects nothing to touch them
until it resumes. Konstantin found three ways this does not hold while
reviewing the VSTOR-151979 series (VSTOR-152985, VSTOR-152984,
VSTOR-152981):

- a submitter racing the stop either runs without the cmd waiting for
  it, or is parked after resume and never completes (patch 1);

- the ploop_allocator() thread is not stopped at all. It truncates the
  top delta while merge, notify_merged or flip moves it in deltas[],
  cutting the live image (patch 3). The thread can also miss a wakeup,
  which stalls the device by itself and would hang the new wait, so
  patch 2 fixes that first;

- a grow failing to copy a cluster resumes submission with that
  cluster's BAT page still busy, and writes to it hang (patch 4).

Patches 1 and 3 both lose data: a pio slipping past the stop can read
and write through a delta that merge has already released, and the
allocator cuts the live image. Patch 3 is the easiest to hit, a
snapshot delete under write load is enough.

Tested on dev-cl04, stock 6.12.0-211.52.1.22.11.vz10, dm-ploop built
out of tree:
- each bug reproduced on the stock module, the races with a test-only
  kprobe module widening the window: a pio running past the suspend of
  a cmd; a pio never completing after resume; the top image truncated
  from 512M to 128M by a merge and to 256M by a flip; after a grow
  failing with ENOSPC on a full host fs, a writer stuck in D state, an
  unsuspendable device and a later cmd failing with ETIMEDOUT. None of
  them reproduce with the series;
- set_noresume, suspend, a grow to 2T, which relocates 8 clusters and
  restarts the allocator, and flip_upper_deltas with the allocator held:
  v1 cut the old top image from 640M to 256M, v2 waits for the allocator
  and the image keeps its data. On a stock kernel the flip oopses
  first: the check in ploop_check_delta_before_flip() walks past the md
  pages of the lower delta once the BAT has grown. The test ran with a
  local fix for that, which will be sent separately;
- fio 4k random reads and writes, O_DIRECT, 1 to 48 jobs, on a fully
  allocated image over brd: IOPS and system CPU stay within the
  run-to-run spread of the stock module. This setup tops out at about
  420K IOPS elsewhere in dm-ploop and would not show a lock taken on
  submission either, so patch 1 keeps that path lockless;
- the ploop pytest suite, ploop and qcow2 formats, passes. A test for
  patch 4 goes to the ploop tests separately.

Changes in v2, after Konstantin's review:
- 1/4: notify_merged named among the cmds hit by the race;
- 2/4: the stall does not end by itself, and the reorder fixes a lost
  kthread_stop() wakeup as well;
- 3/4: also wait for the allocator in ploop_flip_upper_deltas(), as a
  resize of a dm suspended device restarts it after postsuspend; the
  message names notify_merged, which moves the top delta in both
  directions;
- 4/4: unchanged;
- rebased on rh10-6.12.0-211.52.1.22.17.vz10, Reviewed-by tags added
  to 1/4, 2/4 and 4/4.

v1: http://lore.virtuozzo.com/kernel/20261103083642.130885-1-den@openvz.org/

Denis V. Lunev (4):
  dm-ploop: fix pio submission racing with the suspend and resume of a
    cmd
  dm-ploop: fix a lost wakeup of the ploop_allocator() thread
  dm-ploop: wait for the ploop_allocator() thread before changing
    deltas[]
  dm-ploop: fix a failed cluster copy on grow leaving the BAT page busy

 drivers/md/dm-ploop-cmd.c    | 24 ++++++++++++++++++++++--
 drivers/md/dm-ploop-map.c    | 22 +++++++++++++++-------
 drivers/md/dm-ploop-target.c |  4 ++++
 drivers/md/dm-ploop.h        |  1 +
 4 files changed, 42 insertions(+), 9 deletions(-)


base-commit: 95ab11e2c57e8468412ca586d4be8cd75b6bfbf0
-- 
2.53.0

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[Devel] [PATCH hci-8.1 v2 1/4] dm-ploop: fix pio submission racing with the suspend and resume of a cmd

[Denis V. Lunev]

From: Denis V. Lunev <den@openvz.org>

ploop_submit_embedded_pio() tests stop_submitting_pios and then takes a
ref on the current inflight_bios_ref index without deferred_lock. A cmd
sets the flag and flips the index under that lock and then waits only
for the refs of the old index, so:

- a pio that passed the check before the flag was set takes its ref on the
  new index or on the already killed old one. The cmd does not wait for
  it, and it runs while a merge, notify_merged, resize or delta index
  update rewrites the BAT levels and deltas[];

- a pio that saw the flag set is added to llsuspended_pios after resume
  has cleared the flag and drained the list. Nothing drains it until
  the next cmd, the request never completes and a dm suspend of the
  device hangs.

The submission path dropped deferred_lock on purpose when the lists
became lockless, so keep it lockless. Test the flag and take the ref in
one RCU read-side section, and wait for a grace period in the cmd
between setting the flag and flipping the index: a submitter that missed
the flag then holds its ref on the index the cmd waits for. Only a
submitter that saw the flag takes deferred_lock and tests it again
before parking the pio, and resume clears the flag under that lock
before it drains the list.

Fixes: b90109c12b1c ("dm-ploop: convert the rest of the lists to use llist variant")
Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
https://virtuozzo.atlassian.net/browse/VSTOR-152985
Feature: dm-ploop: ploop target driver
Reviewed-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
Reviewed-by: Konstantin Khorenko <khorenko@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 drivers/md/dm-ploop-cmd.c |  7 +++++--
 drivers/md/dm-ploop-map.c | 16 ++++++++++++----
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-ploop-cmd.c b/drivers/md/dm-ploop-cmd.c
index 645c5136e7ba..d85f4d803b61 100644
--- a/drivers/md/dm-ploop-cmd.c
+++ b/drivers/md/dm-ploop-cmd.c
@@ -132,7 +132,7 @@ static void ploop_resume_submitting_pios(struct ploop *ploop)
 	ploop_enable_writeback_delay(ploop);
 	spin_lock_irq(&ploop->deferred_lock);
 	WARN_ON_ONCE(!ploop->stop_submitting_pios);
-	ploop->stop_submitting_pios = false;
+	WRITE_ONCE(ploop->stop_submitting_pios, false);
 	spin_unlock_irq(&ploop->deferred_lock);
 
 	suspended_pending = llist_del_all(&ploop->llsuspended_pios);
@@ -147,9 +147,12 @@ static int ploop_suspend_submitting_pios(struct ploop *ploop)
 	ploop_disable_writeback_delay(ploop);
 	spin_lock_irq(&ploop->deferred_lock);
 	WARN_ON_ONCE(ploop->stop_submitting_pios);
-	ploop->stop_submitting_pios = true;
+	WRITE_ONCE(ploop->stop_submitting_pios, true);
 	spin_unlock_irq(&ploop->deferred_lock);
 
+	/* A submitter that missed the stop gets its ref on the old index */
+	synchronize_rcu();
+
 	ret = ploop_inflight_bios_ref_switch(ploop, true);
 	if (ret)
 		goto out;
diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index 016be97caaa8..f0832fcefeb8 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -2528,6 +2528,7 @@ static void ploop_submit_embedded_pio(struct ploop *ploop, struct pio *pio, gfp_
 	struct ploop_rq *prq = pio->endio_cb_data;
 	struct request *rq = prq->rq;
 	LLIST_HEAD(deferred_pios);
+	unsigned long irqflags;
 	int ret = 0;
 	struct pio *spio;
 
@@ -2538,12 +2539,19 @@ static void ploop_submit_embedded_pio(struct ploop *ploop, struct pio *pio, gfp_
 		pio->queue_list_id = PLOOP_LIST_FLUSH;
 	}
 
-	if (unlikely(ploop->stop_submitting_pios)) {
-		llist_add((struct llist_node *)(&pio->list), &ploop->llsuspended_pios);
-		return;
+	rcu_read_lock();
+	if (unlikely(READ_ONCE(ploop->stop_submitting_pios))) {
+		spin_lock_irqsave(&ploop->deferred_lock, irqflags);
+		if (ploop->stop_submitting_pios) {
+			llist_add((struct llist_node *)(&pio->list), &ploop->llsuspended_pios);
+			spin_unlock_irqrestore(&ploop->deferred_lock, irqflags);
+			rcu_read_unlock();
+			return;
+		}
+		spin_unlock_irqrestore(&ploop->deferred_lock, irqflags);
 	}
-
 	ploop_inc_nr_inflight(ploop, pio);
+	rcu_read_unlock();
 
 	if ((pio->bi_op & REQ_OP_MASK) == REQ_OP_FLUSH || pio->bi_op & REQ_PREFLUSH) {
 		ret = ploop_prepare_flush(ploop, pio);
-- 
2.53.0

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[Devel] [PATCH hci-8.1 v2 2/4] dm-ploop: fix a lost wakeup of the ploop_allocator() thread

[Denis V. Lunev]

From: Denis V. Lunev <den@openvz.org>

ploop_allocator() tests prealloc_size and only then sets itself
TASK_INTERRUPTIBLE before schedule(). A request that lands between the
two finds the thread still running, so wake_up_process() does nothing,
and the thread goes to sleep with the request pending. A pio whose
cluster is past the end of the top delta then waits in
ploop_allocate_cluster() for good: ploop_req_prealloc() does not wake
the thread for a size already requested, so later requests do not end
the stall either. The dispatcher waits for every runner to go idle
before it hands out more work, so the whole device stalls.

The thread tests kthread_should_stop() before setting the task state
too, so a kthread_stop() is lost the same way and the removal of the
device hangs.

Set the task state before testing prealloc_size and
kthread_should_stop().

Fixes: cf489cf22cd5 ("dm-ploop: make filespace preallocations async")
Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
https://virtuozzo.atlassian.net/browse/VSTOR-152984
Feature: dm-ploop: ploop target driver
Reviewed-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
Reviewed-by: Konstantin Khorenko <khorenko@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 drivers/md/dm-ploop-map.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index f0832fcefeb8..e64fd8965d46 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -2325,6 +2325,7 @@ int ploop_allocator(void *data)
 	struct file *file;
 
 	for (;;) {
+		set_current_state(TASK_INTERRUPTIBLE);
 		/* we do not care about exact number here - risk one extra schedule wrt taking the lock */
 		if (ploop->prealloc_size) {
 			__set_current_state(TASK_RUNNING);
@@ -2348,7 +2349,6 @@ int ploop_allocator(void *data)
 			__set_current_state(TASK_RUNNING);
 			break;
 		}
-		set_current_state(TASK_INTERRUPTIBLE);
 		schedule();
 	}
 
-- 
2.53.0

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[Devel] [PATCH hci-8.1 v2 3/4] dm-ploop: wait for the ploop_allocator() thread before changing deltas[]

[Denis V. Lunev]

From: Denis V. Lunev <den@openvz.org>

An allocating pio requests the preallocation of the top delta ahead of
itself and does not wait when its cluster already fits, so the
allocator can still be working when submission is suspended or the
device is dm suspended. It looks up the top delta without a lock and
keeps the pointer and the file across its truncate or fallocate, while
a cmd rewrites deltas[] under neither of its locks:

- merge and notify_merged move the top delta one slot down and zero the
  old slot. The allocator then reads a zero file_size from it and
  truncates the live top image down to the preallocation size, or reads
  a NULL file and oopses;

- flip_upper_deltas swaps the two upper slots of a dm suspended device.
  The allocator computes the new length from the size of the delta now
  on top and truncates the old top one, now holding data below it, to
  that length.

Wait for the allocator to finish in ploop_suspend_submitting_pios()
after the inflight pios are gone, and in ploop_postsuspend() before the
device is marked suspended, which is what the flip checks. No pio can
request a new preallocation after either point, but a resize of a dm
suspended device can, as the grow allocates clusters, so wait in
ploop_flip_upper_deltas() too. Wake the waiters with wake_up(), as the
one in ploop_postsuspend() sleeps uninterruptibly.

Fixes: cf489cf22cd5 ("dm-ploop: make filespace preallocations async")
Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
https://virtuozzo.atlassian.net/browse/VSTOR-152984
Feature: dm-ploop: ploop target driver
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 drivers/md/dm-ploop-cmd.c    | 11 +++++++++++
 drivers/md/dm-ploop-map.c    |  4 ++--
 drivers/md/dm-ploop-target.c |  4 ++++
 drivers/md/dm-ploop.h        |  1 +
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-ploop-cmd.c b/drivers/md/dm-ploop-cmd.c
index d85f4d803b61..29f9a7ee7540 100644
--- a/drivers/md/dm-ploop-cmd.c
+++ b/drivers/md/dm-ploop-cmd.c
@@ -159,6 +159,11 @@ static int ploop_suspend_submitting_pios(struct ploop *ploop)
 
 	ret = wait_event_interruptible(ploop->inflight_md_wq,
 				       !atomic_read(&ploop->inflight_md));
+	if (ret)
+		goto out;
+
+	ret = wait_event_interruptible(ploop->dispatcher_wq_prealloc,
+				       ploop_no_pending_prealloc(ploop));
 out:
 	if (ret)
 		ploop_resume_submitting_pios(ploop);
@@ -1176,6 +1181,12 @@ static int ploop_flip_upper_deltas(struct ploop *ploop)
 	if (ret)
 		return ret;
 
+	/* A resize of the suspended device may have restarted the allocator */
+	ret = wait_event_interruptible(ploop->dispatcher_wq_prealloc,
+				       ploop_no_pending_prealloc(ploop));
+	if (ret)
+		return ret;
+
 	return process_flip_upper_deltas(ploop);
 }
 
diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index e64fd8965d46..ae3e287604b7 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -1233,7 +1233,7 @@ void ploop_should_prealloc(struct ploop *ploop)
 	spin_unlock_irqrestore(&ploop->bat_lock, flags);
 }
 
-static int ploop_no_pending_prealloc(struct ploop *ploop)
+int ploop_no_pending_prealloc(struct ploop *ploop)
 {
 	int ret;
 	unsigned long flags;
@@ -2342,7 +2342,7 @@ int ploop_allocator(void *data)
 					PL_FMT("failed to allocate space: %d\n"),
 					       ploop_device_name(ploop), ret);
 			}
-			wake_up_interruptible(&ploop->dispatcher_wq_prealloc);
+			wake_up(&ploop->dispatcher_wq_prealloc);
 			current_restore_flags(old_flags, PLOOP_PFLAGS);
 		}
 		if (kthread_should_stop()) {
diff --git a/drivers/md/dm-ploop-target.c b/drivers/md/dm-ploop-target.c
index 3b589579741c..d8279c79ef56 100644
--- a/drivers/md/dm-ploop-target.c
+++ b/drivers/md/dm-ploop-target.c
@@ -743,6 +743,10 @@ static void ploop_presuspend_undo(struct dm_target *ti)
 }
 static void ploop_postsuspend(struct dm_target *ti)
 {
+	struct ploop *ploop = ti->private;
+
+	wait_event(ploop->dispatcher_wq_prealloc,
+		   ploop_no_pending_prealloc(ploop));
 	ploop_set_suspended(ti, true);
 }
 static int ploop_preresume(struct dm_target *ti)
diff --git a/drivers/md/dm-ploop.h b/drivers/md/dm-ploop.h
index 7d0d94e7b266..5ae02ef5ffc2 100644
--- a/drivers/md/dm-ploop.h
+++ b/drivers/md/dm-ploop.h
@@ -652,6 +652,7 @@ extern void ploop_disable_writeback_delay(struct ploop *ploop);
 extern void ploop_enable_writeback_delay(struct ploop *ploop);
 
 extern void ploop_should_prealloc(struct ploop *ploop);
+extern int ploop_no_pending_prealloc(struct ploop *ploop);
 extern void ploop_resubmit_enospc_pios(struct ploop *ploop);
 
 #endif /* __DM_PLOOP_H */
-- 
2.53.0

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[Devel] [PATCH hci-8.1 v2 4/4] dm-ploop: fix a failed cluster copy on grow leaving the BAT page busy

[Denis V. Lunev]

From: Denis V. Lunev <den@openvz.org>

ploop_prepare_reloc_index_wb() marks the BAT page of a relocated
cluster MD_UPDATING and MD_DIRTY and allocates the cluster to copy it
to. When ploop_write_cluster_sync() then fails, an I/O error or ENOSPC
on the host file system, ploop_grow_relocate_cluster() only frees the
piwb. The resize fails and submission resumes with both bits set:

- every allocating write, discard or COW on a cluster of that page is
  parked in md->wait_llist, which only a writeback completion of the
  page drains, and none comes. These requests never complete, a dm
  suspend of the device hangs and later ploop cmds time out in the
  inflight ref switch;

- the allocated cluster stays taken in holes_bitmap until the image is
  reopened.

Clear the bits as the error path of ploop_prepare_reloc_index_wb()
does and give the cluster back. Submission is stopped for the whole
resize, so no pio waits on the page and none has to be resubmitted.

Fixes: 018063db0eeb ("dm-ploop: fix resize and grow to use the new way of updating md pages")
Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
https://virtuozzo.atlassian.net/browse/VSTOR-152981
Feature: dm-ploop: ploop target driver
Reviewed-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
Reviewed-by: Konstantin Khorenko <khorenko@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 drivers/md/dm-ploop-cmd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/md/dm-ploop-cmd.c b/drivers/md/dm-ploop-cmd.c
index 29f9a7ee7540..1cb186a2e0cd 100644
--- a/drivers/md/dm-ploop-cmd.c
+++ b/drivers/md/dm-ploop-cmd.c
@@ -351,6 +351,12 @@ static int ploop_grow_relocate_cluster(struct ploop *ploop,
 		PL_ERR("reloc: failed write: %d", ret);
 		/* piwb can not change here we are the only user of md page */
 		ploop_break_bat_update(ploop, md, piwb);
+		spin_lock_irq(&ploop->bat_lock);
+		if (add_for_wb)
+			clear_bit(MD_DIRTY, &md->status);
+		clear_bit(MD_UPDATING, &md->status);
+		ploop_hole_set_bit(new_dst, ploop);
+		spin_unlock_irq(&ploop->bat_lock);
 		goto out;
 	}
 
-- 
2.53.0

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Re: [Devel] [PATCH hci-8.1 v2 1/4] dm-ploop: fix pio submission racing with the suspend and resume of a cmd

[no-reply]

> From: Denis V. Lunev <den@openvz.org>
> 
> ploop_submit_embedded_pio() tests stop_submitting_pios and then takes a
> ref on the current inflight_bios_ref index without deferred_lock. A cmd
> sets the flag and flips the index under that lock and then waits only
> for the refs of the old index, so:
> 
> - a pio that passed the check before the flag was set takes its ref on the
>   new index or on the already killed old one. The cmd does not wait for
>   it, and it runs while a merge, notify_merged, resize or delta index
>   update rewrites the BAT levels and deltas[];
> 
> - a pio that saw the flag set is added to llsuspended_pios after resume
>   has cleared the flag and drained the list. Nothing drains it until
>   the next cmd, the request never completes and a dm suspend of the
> [ ... ]
> https://virtuozzo.atlassian.net/browse/VSTOR-152985
> Feature: dm-ploop: ploop target driver
> Reviewed-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
> Reviewed-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Re: [Devel] [PATCH hci-8.1 v2 2/4] dm-ploop: fix a lost wakeup of the ploop_allocator() thread

[no-reply]

> From: Denis V. Lunev <den@openvz.org>
> 
> ploop_allocator() tests prealloc_size and only then sets itself
> TASK_INTERRUPTIBLE before schedule(). A request that lands between the
> two finds the thread still running, so wake_up_process() does nothing,
> and the thread goes to sleep with the request pending. A pio whose
> cluster is past the end of the top delta then waits in
> ploop_allocate_cluster() for good: ploop_req_prealloc() does not wake
> the thread for a size already requested, so later requests do not end
> the stall either. The dispatcher waits for every runner to go idle
> before it hands out more work, so the whole device stalls.
> 
> The thread tests kthread_should_stop() before setting the task state
> too, so a kthread_stop() is lost the same way and the removal of the
> device hangs.
> 
> Set the task state before testing prealloc_size and
> kthread_should_stop().
> 
> Fixes: cf489cf22cd5 ("dm-ploop: make filespace preallocations async")
> Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> https://virtuozzo.atlassian.net/browse/VSTOR-152984
> Feature: dm-ploop: ploop target driver
> Reviewed-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
> Reviewed-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
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Re: [Devel] [PATCH hci-8.1 v2 3/4] dm-ploop: wait for the ploop_allocator() thread before changing deltas[]

[no-reply]

> From: Denis V. Lunev <den@openvz.org>
> 
> An allocating pio requests the preallocation of the top delta ahead of
> itself and does not wait when its cluster already fits, so the
> allocator can still be working when submission is suspended or the
> device is dm suspended. It looks up the top delta without a lock and
> keeps the pointer and the file across its truncate or fallocate, while
> a cmd rewrites deltas[] under neither of its locks:
> 
> - merge and notify_merged move the top delta one slot down and zero the
>   old slot. The allocator then reads a zero file_size from it and
>   truncates the live top image down to the preallocation size, or reads
>   a NULL file and oopses;
> 
> - flip_upper_deltas swaps the two upper slots of a dm suspended device.
> [ ... ]
> Fixes: cf489cf22cd5 ("dm-ploop: make filespace preallocations async")
> Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> https://virtuozzo.atlassian.net/browse/VSTOR-152984
> Feature: dm-ploop: ploop target driver
> Signed-off-by: Denis V. Lunev <den@openvz.org>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261104185519.1870488-1-den@openvz.org?part=3


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Re: [Devel] [PATCH hci-8.1 v2 4/4] dm-ploop: fix a failed cluster copy on grow leaving the BAT page busy

[no-reply]

> From: Denis V. Lunev <den@openvz.org>
> 
> ploop_prepare_reloc_index_wb() marks the BAT page of a relocated
> cluster MD_UPDATING and MD_DIRTY and allocates the cluster to copy it
> to. When ploop_write_cluster_sync() then fails, an I/O error or ENOSPC
> on the host file system, ploop_grow_relocate_cluster() only frees the
> piwb. The resize fails and submission resumes with both bits set:
> 
> - every allocating write, discard or COW on a cluster of that page is
>   parked in md->wait_llist, which only a writeback completion of the
>   page drains, and none comes. These requests never complete, a dm
>   suspend of the device hangs and later ploop cmds time out in the
>   inflight ref switch;
> 
> - the allocated cluster stays taken in holes_bitmap until the image is
>   reopened.
> 
> Clear the bits as the error path of ploop_prepare_reloc_index_wb()
> does and give the cluster back. Submission is stopped for the whole
> resize, so no pio waits on the page and none has to be resubmitted.
> 
> Fixes: 018063db0eeb ("dm-ploop: fix resize and grow to use the new way of updating md pages")
> Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> https://virtuozzo.atlassian.net/browse/VSTOR-152981
> Feature: dm-ploop: ploop target driver
> Reviewed-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
> Reviewed-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
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Re: [Devel] [PATCH hci-8.1 v2 0/4] dm-ploop: fix the pio submission stop around cmds

[Konstantin Khorenko]

On Wed, 04 Nov 2026 19:55:15 +0100, Denis V. Lunev wrote:
> dm-ploop: fix the pio submission stop around cmds
> 
> A cmd stops pio submission and waits for the inflight pios before it
> rewrites the BAT levels or deltas[], and expects nothing to touch them
> until it resumes. Konstantin found three ways this does not hold while
> reviewing the VSTOR-151979 series (VSTOR-152985, VSTOR-152984,
> VSTOR-152981):
> 
> [...]

Applied to branch-rh10-6.12.0-211.52.1.22.x.vz10-ovz, will be released in rh10-6.12.0-211.52.1.22.18.vz10, thanks!

[1/4] dm-ploop: fix pio submission racing with the suspend and resume of a cmd
      https://bitbucket.org/virtuozzocore/vzkernel.vzs/commits/e136ba445aac
[2/4] dm-ploop: fix a lost wakeup of the ploop_allocator() thread
      https://bitbucket.org/virtuozzocore/vzkernel.vzs/commits/40cdeacffca0
[3/4] dm-ploop: wait for the ploop_allocator() thread before changing deltas[]
      https://bitbucket.org/virtuozzocore/vzkernel.vzs/commits/b1a60171d1ac
[4/4] dm-ploop: fix a failed cluster copy on grow leaving the BAT page busy
      https://bitbucket.org/virtuozzocore/vzkernel.vzs/commits/fd59086034ca

-- 
Konstantin Khorenko,
Virtuozzo Linux Kernel Team


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