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7hz5GoGKbmGmjDTbrrPFj4fVxesPpTo+brOmq57gxfH0uy1oMBDFGETOJ+vgsj4HS1rRg591xYtc65cmWy1t6s+3ueUtByq/g8h+j6B9dLmTJjF8OBTZO7qb4MGvYxnj0kNSeven3EC32Teow1puG0yt787Z9VmYjWnHOpCArAcA9mRVPPPltanROn4Z2j3m70z3Ztw5VXha3M8sNX4OUab8WPKzp9I6Y1xf8FZozkdroTuhzl78tM6ntv/N5U4pWZF6gBnp/PHFVFKP4AsFkh9XKuN78pMZ66PuV2UhR6QoFX/r/dGRHUdkeXIIy4E2l5MyiAGYQ8I5bH3OlF9VNF6D3N9qW5MJ2TVQXNOR0OsLDi77yk2E/LeqSFhV1KRLsLJi58L1PB/Eep/L9DS6t79CCoejixYP6OOvU6V7xjIXJS1A= 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 12 Feb 2025, at 10:32, Dan Carpenter wrote: > On Wed, Feb 12, 2025 at 10:30:26AM -0500, Zi Yan wrote: >> Hi Dan, >> >> Thanks for reporting, but based on __split_unmmaped_folio()’s call site, >> mapping cannot be NULL when it is dereferenced. Is there a proper way to >> tell Smatch that? VM_BUG_ON(folio_test_anon(folio) || !mapping) might >> help the first case, but not sure about the second one. >> > > No, just ignore the warning. I'll probably send another email if you > ever rename the function, but I try not to... Thanks for taking a look > at this. Thanks. I do think these reports are helpful, since they force me to spell out the implications. For the second case, when mapping is NULL __folio_split() sets end to -1 which is the max value of pgoff_t and folio->index would not reach to that value , then in __split_unmapped_folio() at line 3586 in the report, release->index can only be >= end when mapping is not NULL. This means line 3587 can be true and nr_dropped (line 3588) can become non-zero, when mapping is not NULL . I write this down for the record. Best Regards, Yan, Zi