From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ACB9E35DA65; Wed, 10 Jun 2026 23:40:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781134849; cv=none; b=sNhkWQwpBZLUjhn0R2ZNQndP7sUcBwI1TKvH6pplPLDUSyzlQ6LBTPizOv1Tjc5a6M0JwBDR1I91uhlrw+Z6BrAwMzwLBu9nSNPloGOdsA9caR9nH7qAxZnA51ikw3L/SXDoBSlD+D1dx3DEHZtpYG7nMxm9Red1hfrYwI4PrCE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781134849; c=relaxed/simple; bh=lQQ8KdopoOpPrsJ7rhAMPKyWe8FqtnwugRvEHRrHiuU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=F+fpaDXVtmBkzG5C0Ri+UtvenIaqlNhC3GcKOMriyjlyOLn+l/zI1lYi/cUugehNm8dr39YG9XrKNHpnX4Vbk9fqfpGa/XJ/s9k67sv8VUAy1xa77RE/GkDtx4tINQQ/roLBz1GFe2zXyrnTD7B2QUqyYKA5U1fPcRjiobKM8Nk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=D96GS/Zi; arc=none smtp.client-ip=198.175.65.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="D96GS/Zi" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1781134847; x=1812670847; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=lQQ8KdopoOpPrsJ7rhAMPKyWe8FqtnwugRvEHRrHiuU=; b=D96GS/ZirgX9tF+mz+bwsGDfekmL09kq3Yj3RIVkVcSpQVfqW75+8nvG BPyIRO4kVgv/m7sqJODqcqVOyPx6cpMxFnd8z192IyY7RYNtvD6MfJ2BB WXAVhT1uCrJq1JyujKNQQHl86kJFz94wb7RtMGqmP8R1fRnfIeHnj6xCO xtAEZlalFneEyZbCJhYvms0tMLWymvyJWZBJAcYW48YuNmNCM2yB2uzDC DMmoyNrBbC9BlpyZ3JfMo4JxQgJMPEiSB5PsgZuYTcn29ljMyPY7hkhgB Qza4cwnGTQu2qHer923FW3Zyf4TB9liLB3XFsxCzmZoxJYTLTVnD0sd8q Q==; X-CSE-ConnectionGUID: 2FAlSCRnTU+U7eBCbHfGuQ== X-CSE-MsgGUID: /Rkw+VVhQqWh5Sy+fiMODQ== X-IronPort-AV: E=McAfee;i="6800,10657,11813"; a="93050351" X-IronPort-AV: E=Sophos;i="6.24,197,1774335600"; d="scan'208";a="93050351" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jun 2026 16:40:46 -0700 X-CSE-ConnectionGUID: 67A4E6m8Q0eVZ5U1Ujb38g== X-CSE-MsgGUID: 9oaznthFSHqLORHQWWLQIw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.24,197,1774335600"; d="scan'208";a="242176498" Received: from smithj1-mobl2.amr.corp.intel.com (HELO [10.125.110.59]) ([10.125.110.59]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jun 2026 16:40:45 -0700 Message-ID: <58e36b2d-d036-471f-b9ad-87facad01fcc@intel.com> Date: Wed, 10 Jun 2026 16:40:42 -0700 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/5] mm: Add RCU-based VMA lookup helper that waits for writers To: Dave Hansen , linux-kernel@vger.kernel.org Cc: Alice Ryhl , Andrew Morton , =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOl?= =?UTF-8?Q?g?= , Carlos Llamas , Christian Brauner , David Ahern , "David S. Miller" , Greg Kroah-Hartman , "Liam R. Howlett" , linux-mm@kvack.org, Lorenzo Stoakes , netdev@vger.kernel.org, Shakeel Butt , Suren Baghdasaryan , Todd Kjos , Vlastimil Babka References: <20260610230409.A44D29FA@davehans-spike.ostc.intel.com> <20260610230415.C0521C88@davehans-spike.ostc.intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: <20260610230415.C0521C88@davehans-spike.ostc.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/10/26 16:04, Dave Hansen wrote: > + /* Slow path: preclude VMA writers by getting mmap read lock. */ > + guard(rwsem_read)(&mm->mmap_lock); > + if (!vma_start_read_locked(vma)) > + return NULL; Welp, I actually ran and tested this, but it's got a big bug. The slow path is broken. It needs: /* Slow path: preclude VMA writers by getting mmap read lock. */ guard(rwsem_read)(&mm->mmap_lock); + vma = vma_lookup(mm, address); if (!vma_start_read_locked(vma)) return NULL; Because VMA is NULL in slow path otherwise. So it'll definitely need a v3 or a fixup before it goes anywhere.