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Thu, 20 Feb 2025 18:53:08 GMT Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0D4CC20043; Thu, 20 Feb 2025 18:53:08 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3CEE020040; Thu, 20 Feb 2025 18:53:06 +0000 (GMT) Received: from osiris (unknown [9.171.52.26]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTPS; Thu, 20 Feb 2025 18:53:06 +0000 (GMT) Date: Thu, 20 Feb 2025 19:53:04 +0100 From: Heiko Carstens To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, peterz@infradead.org, willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, david.laight.linux@gmail.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, lokeshgidra@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, klarasmodin@gmail.com, richard.weiyang@gmail.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v10 12/18] mm: replace vm_lock and detached flag with a reference count Message-ID: <20250220185304.8313A7d-hca@linux.ibm.com> References: <20250213224655.1680278-1-surenb@google.com> <20250213224655.1680278-13-surenb@google.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250213224655.1680278-13-surenb@google.com> X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: M-vGldV3REsWVvBOwJDEiV9dEv7a8khD X-Proofpoint-GUID: LuM4Ib9qTs5DatP339mkaUEvtZKh3JTf 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=2025-02-20_08,2025-02-20_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 priorityscore=1501 suspectscore=0 bulkscore=0 mlxscore=0 adultscore=0 spamscore=0 impostorscore=0 phishscore=0 clxscore=1011 lowpriorityscore=0 mlxlogscore=842 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502100000 definitions=main-2502200128 On Thu, Feb 13, 2025 at 02:46:49PM -0800, Suren Baghdasaryan wrote: ... > While this vm_lock replacement does not yet result in a smaller > vm_area_struct (it stays at 256 bytes due to cacheline alignment), it > allows for further size optimization by structure member regrouping > to bring the size of vm_area_struct below 192 bytes. > > Suggested-by: Peter Zijlstra > Suggested-by: Matthew Wilcox > Signed-off-by: Suren Baghdasaryan > --- > Changes since v9 [1]: > - Use __refcount_inc_not_zero_limited_acquire() in vma_start_read(), > per Hillf Danton > - Refactor vma_assert_locked() to avoid vm_refcnt read when CONFIG_DEBUG_VM=n, > per Mateusz Guzik > - Update changelog, per Wei Yang > - Change vma_start_read() to return EAGAIN if vma got isolated and changed > lock_vma_under_rcu() back to detect this condition, per Wei Yang > - Change VM_BUG_ON_VMA() to WARN_ON_ONCE() when checking vma detached state, > per Lorenzo Stoakes > - Remove Vlastimil's Reviewed-by since code is changed This causes crashes (NULL pointer deref) with linux-next when running the ltp test suite; mtest06 (mmap1) test case. The bug seems to be quite obvious: > @@ -6424,15 +6492,18 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, > if (!vma) > goto inval; > > - if (!vma_start_read(vma)) > - goto inval; > + vma = vma_start_read(vma); > + if (IS_ERR_OR_NULL(vma)) { ^^^^^^^^^^^^^^^^^^^ > + /* Check if the VMA got isolated after we found it */ > + if (PTR_ERR(vma) == -EAGAIN) { > + vma_end_read(vma); ^^^^^^^^^^^^^^^^