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b=mjyHxqXBTuL/C33GIeEKXv9J+4fm0TfyMtimPLBVg2RohCxzJRquEGeDJY9Lp1zVc nwMQBzXTIgs7z9wUQtt8X7WUIjDWQYSCwqLLkVSbCbrqFuuWd8JQp8BUp4JAQq3TBd cP1m3iJd7zDuCwy1LtJ+Ku9wkEiPvj0qgvucCFDc= Date: Wed, 7 May 2025 17:34:57 -0700 From: Andrew Morton To: Shivank Garg Cc: Dan Carpenter , oe-kbuild@lists.linux.dev, lkp@intel.com, oe-kbuild-all@lists.linux.dev, Linux Memory Management List Subject: Re: [linux-next:master 7893/8235] fs/jfs/jfs_metapage.c:245 __metapage_migrate_folio() error: we previously assumed 'mp' could be null (see line 235) Message-Id: <20250507173457.d2c6eb2b92a10fbd4185cf1f@linux-foundation.org> In-Reply-To: <21037c25-b85c-48fa-bdac-27cb3be2ccdb@amd.com> References: <202505071850.XaOkcCkX-lkp@intel.com> <21037c25-b85c-48fa-bdac-27cb3be2ccdb@amd.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: AD7E040004 X-Stat-Signature: abnd6wpmqo3sxc5wjt979no3qe1csmke X-Rspam-User: X-HE-Tag: 1746664499-642733 X-HE-Meta: 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 PxHkhTHQ g59hOrnP4HLaXjqwskXYDlh/gnwi9b1yDm/oJp5MNdhUy7zNwI/jKMc+wqs8DP+m8vnfKPLmJ9B8R4UjE9WEuuQ91KCvvvShhcjdsnC9e8FeUSXZyW62tXu1JLJhxrnXkhGvmxeS0n4al/ePQG3xl7JwdLkCIYJ9NeamurBTCtb/y8b15SnC/IhxoMTLm1Pwx9RfbfA8uWGI+BJxpZfV+Uav6MGj7nrMp6devERS5JycGZznLAm3UTCp/Siayt4m4YktSfYBXFq7e7hhRldKYQOMDelBJ7KahNBxEqsJv6KbxUwM2mcwqai5RNskGK3Uspazs X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 7 May 2025 17:19:52 +0530 Shivank Garg wrote: > This is a false positive. > > In metapage_migrate_folio(), it checks if (!src->private) and only calls > __metapage_migrate_folio() if src->private is non-NULL > > static int metapage_migrate_folio(struct address_space *mapping, struct folio *dst, > struct folio *src, enum migrate_mode mode) > { > ... > if (!src->private) > return filemap_migrate_folio(mapping, dst, src, mode); > ... > ... > return __metapage_migrate_folio(mapping, dst, src, mode); > } > > Then __metapage_migrate_folio() calls mp = folio_to_mp(src, 0), which returns src->private. > Which should not be NULL as previously checked. > > I think we can skip the mp != NULL check from > > 39ed4d1a0e03ce Shivank Garg 2025-04-30 @235 if (mp && metapage_locked(mp)) > It seem redundant here. Yes. Right now the code simply looks wrong: mp = folio_to_mp(src, 0); if (mp && metapage_locked(mp)) return -EAGAIN; ... page_offset = mp->data - folio_address(src); any reader of this will be worried. A code comment (at least) would save them concern and time. Reworking the code to eliminate doubt would be better.