Re: [v3 PATCH] rhashtable: Fix rhashtable_try_insert test
From: Zaslonko Mikhail <hidden>
Date: 2025-01-17 13:21:04
Also in:
linux-crypto, linux-hyperv, lkml
Hello, On 14.01.2025 04:15, Herbert Xu wrote:
On Fri, Jan 10, 2025 at 06:22:40PM +0000, Michael Kelley wrote: Thanks for testing! The patch needs one more change though as moving the atomic_inc outside of the lock was a bad idea on my part. This could cause atomic_inc/atomic_dec to be reordered thus resulting in an underflow. Thanks,
I've tested v3 patch on s390 for the boot OOM problem with 'mem=1G' kernel parameter we experience on current linux-next kernel and confirm that the issue is no longer present. Tested-by: Mikhail Zaslonko <redacted>
quoted hunk ↗ jump to hunk
---8<--- The test on whether rhashtable_insert_one did an insertion relies on the value returned by rhashtable_lookup_one. Unfortunately that value is overwritten after rhashtable_insert_one returns. Fix this by moving the test before data gets overwritten. Simplify the test as only data == NULL matters. Finally move atomic_inc back within the lock as otherwise it may be reordered with the atomic_dec on the removal side, potentially leading to an underflow. Reported-by: Michael Kelley <redacted> Fixes: e1d3422c95f0 ("rhashtable: Fix potential deadlock by moving schedule_work outside lock") Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>diff --git a/lib/rhashtable.c b/lib/rhashtable.c index bf956b85455a..0e9a1d4cf89b 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c@@ -611,21 +611,23 @@ static void *rhashtable_try_insert(struct rhashtable *ht, const void *key, new_tbl = rht_dereference_rcu(tbl->future_tbl, ht); data = ERR_PTR(-EAGAIN); } else { + bool inserted; + flags = rht_lock(tbl, bkt); data = rhashtable_lookup_one(ht, bkt, tbl, hash, key, obj); new_tbl = rhashtable_insert_one(ht, bkt, tbl, hash, obj, data); + inserted = data && !new_tbl; + if (inserted) + atomic_inc(&ht->nelems); if (PTR_ERR(new_tbl) != -EEXIST) data = ERR_CAST(new_tbl); rht_unlock(tbl, bkt, flags); - if (PTR_ERR(data) == -ENOENT && !new_tbl) { - atomic_inc(&ht->nelems); - if (rht_grow_above_75(ht, tbl)) - schedule_work(&ht->run_work); - } + if (inserted && rht_grow_above_75(ht, tbl)) + schedule_work(&ht->run_work); } } while (!IS_ERR_OR_NULL(new_tbl));
Thanks!