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Tue, 11 Aug 2026 14:12:04 +0000 (GMT) Received: from osiris (unknown [9.87.143.60]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTPS; Tue, 11 Aug 2026 14:12:04 +0000 (GMT) Date: Tue, 11 Aug 2026 16:12:03 +0200 From: Heiko Carstens To: Alexander Gordeev 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: <20260811141203.12308B7d-hca@linux.ibm.com> References: <20260811121316.2622460-1-agordeev@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: <20260811121316.2622460-1-agordeev@linux.ibm.com> X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=XqfK/1F9 c=1 sm=1 tr=0 ts=6a7b2db9 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=kj9zAlcOel0A:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=RPZ-f58JHGKQJTKQA7MA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODExMDExNyBTYWx0ZWRfX41J/suBnxx5p RJKtYn4GPAhbPy6eDZ6rqnH17UqMMY20aX2nHM/lWW2GkQeDQvDM2arrrf9rd7Gse2mbzHa7+Ko gAEmIUncDzqOJmFiE9ZcmFj7Hi+17oI9+lTs24hBmOU8SQIUKWgmj3SHSwi4uyr8CtG5+9riuSf GjIlUtIn51nLbP93U6HDD6E4vsRbJRLzxArVNMPcCkwSlrcboqHoJaeaP4xDLFnCD108MRI66N0 5cPNeJTCMKccC4bKC4TGjTXNdFNOfyCu21csYPC+qBek4hTJ9SrUkktsckX/oZMofuZlG5gOqpG jewUYKd7p8IIZ4vJrMzzTqR5JEaa8PpnWdvMIZu6NsN4mRCLFur3O9KZv5AzJOBn/1RwhIErg+q Q2e5//6ItLAFycWy0ngC61jZ8T5ShASzAPQPvN7k2S9+4DrIK8EdSro8BaawhBdKxz12x2QjMCm Nl+UoJrXT4fD+Z+9slw== X-Proofpoint-ORIG-GUID: FRgG_mWd1kqjP4CrAzwZstBYdH5zyRKR X-Proofpoint-GUID: FRgG_mWd1kqjP4CrAzwZstBYdH5zyRKR X-Proofpoint-Spam-Info: AW1haW4tMjYwODExMDExNyBTYWx0ZWRfX2z4NvL6iEDda Z4IWewp2mQh4V6+dBINyceO23i855l0L/Co5kbvwt0YW+dzHDiUnmlst9FM/9VYCzwgGOy0QQU0 CKUpveQ2D1DszVcllnrpxb0youzdZUw= 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=2026-08-11_03,2026-08-10_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 spamscore=0 adultscore=0 malwarescore=0 clxscore=1015 suspectscore=0 priorityscore=1501 impostorscore=0 phishscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608110117 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. [1] 31932757c612 ("s390/mm: optimize page table upgrade routine") [2] b5efb63acf7b ("s390/mm: Add NULL pointer check to crst_table_free() base_crst_free()")