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Wed, 19 Aug 2026 11:22:51 +0000 (GMT) Received: from li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com (unknown [9.224.92.206]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTPS; Wed, 19 Aug 2026 11:22:51 +0000 (GMT) Date: Wed, 19 Aug 2026 13:22:50 +0200 From: Alexander Gordeev To: Heiko Carstens Cc: Gerald Schaefer , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] s390/mm: Fix fail path in crst_table_upgrade() Message-ID: <9e707e9c-2da5-4325-9bf3-b41aefb2f8ab-agordeev@linux.ibm.com> References: <20260811121316.2622460-1-agordeev@linux.ibm.com> <20260811141203.12308B7d-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260811141203.12308B7d-hca@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Info: AW1haW4tMjYwODE5MDA4NSBTYWx0ZWRfXw8gtIIbYoAKA 9WT55qNS+KAWyXqXG7PptrcK2tQn2Qu1mi6YiBDhGkSE5ewiAuZjUjt95I0Ojy96qZEhSJjw8Ip 4HY0CP7lz5iJPNOnQA4daND2RgXSlF4= X-Proofpoint-GUID: veCJnSX8UJ4GnSxBgynb19oHvKeB3W8G X-Proofpoint-ORIG-GUID: veCJnSX8UJ4GnSxBgynb19oHvKeB3W8G X-Authority-Analysis: v=2.4 cv=RPmD2Yi+ c=1 sm=1 tr=0 ts=6a859210 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=kj9zAlcOel0A:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=hJ7KTuLPrbn1ANyxZ0cA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE5MDA4NSBTYWx0ZWRfXwCrBTcoa/SQI MOaCTVEcqYKvdkUp08O9SnUsItZbNZsa2RUs1q9MvE4s9QVg2RF/QA+lQFSaaq0T4LmCxQjS4cC KFvIwogygF2RyWSGoZmwpfGZ909W9edy2xxs8V8YP8tE2IQUNqr1dEbMfGv0X5pyhYZWbvyvIa0 XAWYq9utW6G0mRCmuaRcD5gp6PlJGk8Yj2gMSBBWmFb0muFiVK62xglzcJmx2yQcwAC9rXml1L4 3uV236Wy1asXLExinVtnw3gsC4ljv/g4jsCYWxhnWj7vs1tAFKXnqcyqoNhoy+YiWRF0Vlmeo6j rcVB7ROfMsA+MMcF7gA2s+z7FiZgA3SCWwfsQXA6GV+eN0Edf4waTDAmsZy+uoTkoXlx9m8AI5P Lr7nLdxnuGbPdQsWtYnOr91vzzwB+A0ZNR1BEK3twtN2UEXz1UI5spEsxQ0/IDJI2WskN+W+t4U y3/dQ2EB4YLo3qmAYEQ== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-19_03,2026-08-18_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 phishscore=0 adultscore=0 spamscore=0 priorityscore=1501 bulkscore=0 impostorscore=0 malwarescore=0 lowpriorityscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608190085 On Tue, Aug 11, 2026 at 04:12:03PM +0200, Heiko Carstens wrote: > On Tue, Aug 11, 2026 at 02:13:16PM +0200, Alexander Gordeev wrote: > > On a 4-to-5 level upgrade (unlike 3-to-5) p4d local variable > > stays NULL. If the pgd allocation then fails, the fault code > > path calls pagetable_dtor(virt_to_ptdesc(p4d)) with NULL. > > > > Fixes: 502269ab98b5 ("s390/mm: add missing ctor/dtor on page table upgrade") > > Signed-off-by: Alexander Gordeev > > --- > > arch/s390/mm/pgalloc.c | 17 ++++++++--------- > > 1 file changed, 8 insertions(+), 9 deletions(-) > > > > diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c > > index 9610770fcf6d..87a8bdb3e51e 100644 > > --- a/arch/s390/mm/pgalloc.c > > +++ b/arch/s390/mm/pgalloc.c > > @@ -69,14 +69,19 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end) > > if (asce_limit == _REGION2_SIZE) { > > p4d = crst_table_alloc(mm); > > if (unlikely(!p4d)) > > - goto err_p4d; > > + return -ENOMEM; > > crst_table_init(p4d, _REGION2_ENTRY_EMPTY); > > pagetable_p4d_ctor(virt_to_ptdesc(p4d)); > > } > > if (end > _REGION1_SIZE) { > > pgd = crst_table_alloc(mm); > > - if (unlikely(!pgd)) > > - goto err_pgd; > > + if (unlikely(!pgd)) { > > + if (p4d) { > > + pagetable_dtor(virt_to_ptdesc(p4d)); > > + crst_table_free(mm, p4d); > > + } > > + return -ENOMEM; > > + } > > crst_table_init(pgd, _REGION1_ENTRY_EMPTY); > > pagetable_pgd_ctor(virt_to_ptdesc(pgd)); > > } > > @@ -106,12 +111,6 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end) > > on_each_cpu(__crst_table_upgrade, mm, 0); > > > > return 0; > > - > > -err_pgd: > > - pagetable_dtor(virt_to_ptdesc(p4d)); > > - crst_table_free(mm, p4d); > > -err_p4d: > > - return -ENOMEM; > > } > > Imho this makes the code even more uglier than it is/was. This is also yet > another bug which is/was only possible after loop unrolling happened with > [1]. Another bug, which would not have been possible without the rework back > then, is [2]. > > So I would _much_ rather prefer to go back to what we had with [1], of course > including the additional dtor/ctor code. But that code was much more readable > compared to what we have now, especially considering the additional fix which > is proposed now. Frankly, to me personally the old version is more difficult to read. In addition, in case of 3-5 upgrade on 4-5 allocation failure it has (a) 4-level table leak and (b) useless 3-4 upgrade. Should all of those get fixed, I doubt the end result will look as simple as the original version. But I can try if you insist. > [1] 31932757c612 ("s390/mm: optimize page table upgrade routine") > [2] b5efb63acf7b ("s390/mm: Add NULL pointer check to crst_table_free() base_crst_free()") Thanks!