在 2021/11/23 10:59, Jianhua1 Hao 郝建华 via Linux-erofs 写道:
*We also found that it is easy to cause deadlock in the kswap scene，
We observed the following deadlock in the stress test under low memory
scenario，****Same as "erofs: fix deadlock when shrink erofs slab".*
**
Thread A: Thread B:
erofs_try_to_release_workgroup(grp =
0xFFFFFF87ADFEE610)erofs_insert_workgroup()
erofs_workgroup_try_to_freeze(grp, 1)//xa lock is held here
//set ref count to EROFS_LOCKED_MAGICxa_lock(&sbi->managed_pslots);
atomic_cmpxchg(&grp->refcount, val,EROFS_LOCKED_MAGIC)pre =
__xa_cmpxchg(&sbi->managed_pslots, grp->index, NULL, grp, GFP_NOFS);
xa_erase(&sbi->managed_pslots, grp->index)erofs_workgroup_get(pre)
//pre = grp = 0xFFFFFF87ADFEE610
//stuck there to wait for xa lock, already held by thread
Berofs_wait_on_workgroup_freezed(grp);
xa_lock(xa); //wait ref count to be unlocked, which should be done by
thread A
atomic_cond_read_relaxed(&grp->refcount, VAL != EROFS_LOCKED_MAGIC);
Follow-up fix:it need to hold the xa lock before freeze the workgroup
beacuse we will operate xarry?
Hi, JianHua,
The fix is in the patch, please test it kindly if you have condition.
https://lore.kernel.org/linux-erofs/YZcJpDs3FKpSfzAE@B-P7TQMD6M-0146/T/#t
---
fs/erofs/utils.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
index 84da2c280012..84a59f075dd1 100644
--- a/fs/erofs/utils.c
+++ b/fs/erofs/utils.c
@@ -150,7 +150,7 @@ static bool erofs_try_to_release_workgroup(struct
erofs_sb_info *sbi,
* however in order to avoid some race conditions, add a
* DBG_BUGON to observe this in advance.
*/
- DBG_BUGON(xa_erase(&sbi->managed_pslots, grp->index) != grp);
+ DBG_BUGON(__xa_erase(&sbi->managed_pslots, grp->index) != grp);
/* last refcount should be connected with its managed pslot. */
erofs_workgroup_unfreeze(grp, 0);
@@ -165,15 +165,20 @@ static unsigned long
erofs_shrink_workstation(struct erofs_sb_info *sbi,
unsigned int freed = 0;
unsigned long index;
+ xa_lock(&sbi->managed_pslots);
xa_for_each(&sbi->managed_pslots, index, grp) {
/* try to shrink each valid workgroup */
if (!erofs_try_to_release_workgroup(sbi, grp))
continue;
+ xa_unlock(&sbi->managed_pslots);
++freed;
if (!--nr_shrink)
- break;
+ return freed;
+ xa_lock(&sbi->managed_pslots);
}
+ xa_unlock(&sbi->managed_pslots);
+
return freed;
}
Thanks,
Jianan
------------------------------------------------------------------------
Jianhua1 Hao
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