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Fri, 17 Jan 2025 13:20:50 GMT Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7063558059; Fri, 17 Jan 2025 13:20:50 +0000 (GMT) Received: from smtpav02.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B4F0058058; Fri, 17 Jan 2025 13:20:47 +0000 (GMT) Received: from [9.171.10.145] (unknown [9.171.10.145]) by smtpav02.wdc07v.mail.ibm.com (Postfix) with ESMTPS; Fri, 17 Jan 2025 13:20:47 +0000 (GMT) Message-ID: <0749cd68-c5ab-4ab6-9c48-6e445263333b@linux.ibm.com> Date: Fri, 17 Jan 2025 14:20:46 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [v3 PATCH] rhashtable: Fix rhashtable_try_insert test To: Herbert Xu , Michael Kelley Cc: Breno Leitao , "saeedm@nvidia.com" , "tariqt@nvidia.com" , "linux-hyperv@vger.kernel.org" , Andrew Morton , Thomas Graf , Tejun Heo , Hao Luo , Josh Don , Barret Rhoden , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Linux Crypto Mailing List References: <20241128-scx_lockdep-v1-1-2315b813b36b@debian.org> <20250102-daffy-vanilla-boar-6e1a61@leitao> <20250109-marigold-bandicoot-of-exercise-8ebede@leitao> Content-Language: en-US From: Zaslonko Mikhail In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: SfzBTF39apMgRV92JDaLcMDIDNyBIFLg X-Proofpoint-ORIG-GUID: rL4d-Rmr_WWKK3HQ6hGm2fGBG1kY_hF8 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-01-17_05,2025-01-16_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 suspectscore=0 clxscore=1011 malwarescore=0 phishscore=0 lowpriorityscore=0 spamscore=0 impostorscore=0 mlxscore=0 priorityscore=1501 bulkscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2411120000 definitions=main-2501170105 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 > > ---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 > Fixes: e1d3422c95f0 ("rhashtable: Fix potential deadlock by moving schedule_work outside lock") > Signed-off-by: Herbert Xu > > 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!