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Tue, 24 Mar 2026 16:47:04 +0530 (IST) Message-ID: <9bf5d3f5-af3f-40ce-b7aa-35b105b8b772@zohomail.in> Date: Tue, 24 Mar 2026 16:47:04 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 2/6] mm/vmalloc: fix vrealloc() grow-in-place check To: Alice Ryhl Cc: Andrew Morton , Uladzislau Rezki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Danilo Krummrich References: <20260324-vmalloc-shrink-v7-0-c0e62b8e5d83@zohomail.in> <20260324-vmalloc-shrink-v7-2-c0e62b8e5d83@zohomail.in> Content-Language: en-US From: Shivam Kalra In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ZohoMailClient: External X-Rspam-User: X-Stat-Signature: dz4jrmsacm7j9x3t15m1nhbpatoupwff X-Rspamd-Queue-Id: F1041A0002 X-Rspamd-Server: rspam09 X-HE-Tag: 1774351050-627966 X-HE-Meta: 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 2eIK7ryI f4IlFRa1fhLIUU7T1pFFrBGmR021ltmK58mvB52akdaZLGSOeo3rxJzY7OKKjnGqBVvtcEsIeTnhrqmtLQxQvbybNsiXRAJRKDXjOsfkBz6Ou9ePIIXNgMTAqLG8PIY0bjlhsLoA9iAhnxWKz6Ln27Pvf7JNKLiUNBJKP05trj+LXQwp3oL5EyI9Ii/QE4GIZw8FppO3WrC2Qfa2tYgYM5QSHRGvSPknhQ70tT8KM7t63XXykkZcMq+oJEpE6MMxrvDyXZb+e2E5zRa5E6yF5n76GBFWvmwRv0Jf5VlACAmjf1+zMaICTno6QXNnXUC+jqeYS9G7EvTD5E5OX5lfY5WN5gwyB4JNfMG28azFZ35dXQdQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 24/03/26 16:31, Alice Ryhl wrote: > On Tue, Mar 24, 2026 at 03:30:27PM +0530, Shivam Kalra via B4 Relay wrote: >> From: Shivam Kalra >> >> Fix the grow-in-place check in vrealloc() to compare the requested size >> against the actual physical page count (vm->nr_pages) rather than the >> virtual area size (alloced_size, derived from get_vm_area_size()). >> >> The virtual reservation size (get_vm_area_size()) does not decrease when >> pages are freed during a shrink operation. Consequently, without this fix, >> a subsequent grow-in-place operation after a shrink would incorrectly >> succeed and attempt to access freed pages. Correcting this check is a >> prerequisite for the upcoming vrealloc() shrink functionality. >> >> Signed-off-by: Shivam Kalra > > This commit is titled 'fix', but is it actually a fix for a bug that > exists today? Or is it just a refactor to support the follow-up > shrinking logic? > > Alice You're right, this is not a fix for a bug that exists today. Currently get_vm_area_size() and vm->nr_pages << PAGE_SHIFT always return the same value because no code frees tail pages from a live vmalloc allocation. The two expressions only diverge once the shrink patch (patch 5/6) is applied, which reduces nr_pages while keeping vm->size unchanged. I'll retitle this to something like: mm/vmalloc: base vrealloc() grow-in-place check on nr_pages and rephrase the commit message to describe it as a preparatory change rather than a fix. Thanks for catching this.