On 7/8/25 03:47, Konstantin Khorenko wrote:
From: Pavel Tikhomirov <ptikhomi...@virtuozzo.com>
Just a cleanup/simplification, no logic changed.
I would argue with that no logic is changed, it is changed.
First we actually fix excess spin_lock/unlock contention. Now lock is
only released when we need it to run ploop_truncate_prealloc_safe(),
which can sleep.
Second, and most importantly, we fix possible race between prealloc_size
check for zero and resetting prealloc_in_progress and prealloc_size.
Previously we could've lost some preallocation requests due to this race
as the bat_lock was released between the check and reset.
https://virtuozzo.atlassian.net/browse/VSTOR-108868
Co-developed-by: Andrey Zhadchenko <andrey.zhadche...@virtuozzo.com>
Signed-off-by: Pavel Tikhomirov <ptikhomi...@virtuozzo.com>
Feature: dm-ploop: ploop target driver
---
drivers/md/dm-ploop-map.c | 12 +++---------
1 file changed, 3 insertions(+), 9 deletions(-)
diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index f7bb6bcf13feb..b59e0d514c95f 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -1172,10 +1172,10 @@ static int ploop_preallocate_cluster(struct ploop
*ploop, struct file *file)
struct ploop_delta *top = ploop_top_delta(ploop);
loff_t end;
unsigned long flags;
- int ret, more = 0;
+ int ret;
-prealloc_more:
spin_lock_irqsave(&ploop->bat_lock, flags);
+prealloc_more:
ploop->prealloc_in_progress = ploop->prealloc_size;
end = top->file_size + ploop->prealloc_in_progress;
loff_t new_len = ALIGN(end, ploop->prealloc_in_progress);
@@ -1190,6 +1190,7 @@ static int ploop_preallocate_cluster(struct ploop *ploop,
struct file *file)
new_len, file, __func__);
if (ret) {
PL_ERR("Failed to preallocate space: %d\n", ret);
+ spin_lock_irqsave(&ploop->bat_lock, flags);
goto out;
}
@@ -1201,15 +1202,8 @@ static int ploop_preallocate_cluster(struct ploop *ploop, struct file *file)
PL_ERR("unexpected file size change\n");
}
if (ploop->prealloc_size)
- more = 1;
- spin_unlock_irqrestore(&ploop->bat_lock, flags);
- if (more) {
- more = 0;
goto prealloc_more;
- }
-
out:
- spin_lock_irqsave(&ploop->bat_lock, flags);
ploop->prealloc_in_progress = 0;
ploop->prealloc_size = 0;
spin_unlock_irqrestore(&ploop->bat_lock, flags);
--
Best regards, Pavel Tikhomirov
Senior Software Developer, Virtuozzo.
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