From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f73.google.com (mail-wm1-f73.google.com [209.85.128.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0FF2D3D76 for ; Sun, 22 Mar 2026 12:48:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774183713; cv=none; b=ag5S+Dr1O5vRPmhUh7RVuOLjvBhbmjGgT+md7M2J+cNSS0mX9blJx8IlEffSDem0+6bGIH2p9a79TElc72IC4v4ST9YnrYmivttwEKiM5xRqN6caUf2JYU5kjp+yUv2WEPUv6cmL16XMGhkaCaevbwILi1L1A4qvUiyfFh2tSwE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774183713; c=relaxed/simple; bh=yCw7py3X3fPgmThbwDX1pcEV5A69O4qnmDruDjqUJM4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=segNP0S4EjgUa2NcskP20a50UDpdMIm/S12kzt/eNpp3uSGuhaWku5/oFLqugfqgWqIeYWMJYWyXZ4v/QvGOO739eRXiBxcq4dSlLWrB4eCxHNpHkv40q19rw7pXB6/ugLWxtm9kVwnT5s/MmKIRLgjHW1iNG3MTBKxP+93J3Tg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--aliceryhl.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=wYhDNWp7; arc=none smtp.client-ip=209.85.128.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--aliceryhl.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="wYhDNWp7" Received: by mail-wm1-f73.google.com with SMTP id 5b1f17b1804b1-48553fdd03dso18906265e9.0 for ; Sun, 22 Mar 2026 05:48:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1774183710; x=1774788510; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=qpx8itHUDRTfAnvxzR4PgzdVeXBjt9eZaf3iKVFScbk=; b=wYhDNWp76TIBZECexeIAPXck1GDHaveFp2JICjd48fVuufZFKKVbket1cB0bL6i7ow ZjNaSWP3UTNVBraNmBsh+NIZZDO8VEWqqjQ+XArpnucdwEEjmrbDzOenuAHAf4B1U2Yr OlLPGVOI4/wEePgXvraFtqhZbmraoQKczdIf8/2FfP/XEn/KrX0JotwdpcJ/6/54MR4E JXs0oPKVVhf/ecuF+IXBz7bQS85dKcvj1dGKs1nGp0GqGAP/RVDGDyjeYzpnWKpBwGFz lp8PCOBqHm/SPDHBPVgpTu+7BSDgOGPHpwfPUlNYVHPCU9PVOTMAzoM/SMvtsbC6b+lM 2cPg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774183710; x=1774788510; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=qpx8itHUDRTfAnvxzR4PgzdVeXBjt9eZaf3iKVFScbk=; b=RHNxz8virAgyezY9xmYBI3Y24uLqJ5Qm88U2PH3V47UkeUUMwXjYCWGlY1oDHms8sg 8gTwirllmJ4lt9SqVH1xbk11ci07SiFDKFbJPRRXDEmVuMv9/isR4xJ7qJxYQOuZSrbh bLfibHyOEXaPQTrXDFtdQxqyJyyhkEaiM1gHOyNKW2QJOyclWusjGFuLib8NtOUR5Ynd wapoQfZ5vPJtQzIEo7WXOGFBLYMQg5JrQAYAyPMJrNhoTCdAvJFFvtyAC0OPrnooOpdY vKZn2HNKfZrEEU3BxuBBXQ5WYOP9Tl9Q3Bcs8OSjnii6XPl4Ulti2ll7cFSTAFESaFkw laSA== X-Forwarded-Encrypted: i=1; AJvYcCXqryucmL/milc0wZ925zMkYNYEZYDFBjUn+MZXKqzKLGgmscJz/VAGQC+maBDrp4LmKz1JRyCGqNTPJNA=@vger.kernel.org X-Gm-Message-State: AOJu0Yyishv32BuRC3rlyMHTSJYdiWpZ9oxK8+BrnwpDJSepWjcelWy0 mkY7oqxpnblYV4pnGXq4g9ZqekKajtOx4vMV276pks77XrQzUhxBs+BETeUYyRFd9VH2r9Bg8/D Pt9aAYQcGAthybQIxyQ== X-Received: from wmma23.prod.google.com ([2002:a05:600c:2257:b0:485:3c21:d5f0]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:a69d:b0:487:288:1198 with SMTP id 5b1f17b1804b1-487028812b5mr62847955e9.22.1774183710349; Sun, 22 Mar 2026 05:48:30 -0700 (PDT) Date: Sun, 22 Mar 2026 12:48:28 +0000 In-Reply-To: <03262674-2df0-40d8-b411-4735c6f43770@zohomail.in> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260317-vmalloc-shrink-v5-0-bbfbf54c5265@zohomail.in> <03262674-2df0-40d8-b411-4735c6f43770@zohomail.in> Message-ID: Subject: Re: [PATCH v5 0/3] mm/vmalloc: free unused pages on vrealloc() shrink From: Alice Ryhl To: Shivam Kalra Cc: Andrew Morton , Uladzislau Rezki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Danilo Krummrich Content-Type: text/plain; charset="utf-8" On Sat, Mar 21, 2026 at 01:45:35PM +0530, Shivam Kalra wrote: > On 17/03/26 13:47, Shivam Kalra via B4 Relay wrote: > 3. Fixing a /proc/vmallocinfo race condition > `show_numa_info()` iterates over `v->nr_pages`. During a shrink, > modifying `nr_pages` and NULL-ing out the page pointers concurrently > could cause a reader to dereference a NULL page pointer. > Plan: I'll update the reader to use `READ_ONCE(v->nr_pages)`, and have > the shrink path do a `WRITE_ONCE(vm->nr_pages, new_nr_pages)` before > freeing the pages. This guarantees that concurrent readers either see > the old count with valid pages or the new, smaller count. This doesn't fix the race. Consider this: nr < vm->nr_pages == true vm->nr_pages = nr free vm->pages[nr] page_to_nid(v->pages[nr]) // UAF perhaps changing vm->nr_pages should happen under the vn->busy.lock spinlock? show_numa_info() is called under that lock too. Alice