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AJvYcCVmLpqraVbi0kB5GselixyjSOTL++ZCMCgooJBV25MA8cYZcM5O073LmmAgBp9SRgJm6xLdqabK7g==@kvack.org X-Gm-Message-State: AOJu0YxD6cXvqBfQhVOvOrDHBISY9yuhc6MzJ1gKa5T4lcdEl+XSeeAZ wYEiy7zJaA/VNY3EhZZB8974rmFElaFog9TdYMcAD0YYMBfH7aGG89NFh+SZXYaC07oyYvcDs4t O+07Omk8YazrJSfSWHXioxCPndVc= X-Google-Smtp-Source: AGHT+IENb5DYPovjDFMjwqzq3uvD4Nv2Ze4DbhBh4gLv4aruNViDXNpg95ZVdQIT4X89mk0e7YdoQ5zVz6TsbTbh4PE= X-Received: by 2002:a05:6102:e13:b0:48f:df71:17e3 with SMTP id ada2fe7eead31-497799fe285mr11313058137.28.1724104131684; Mon, 19 Aug 2024 14:48:51 -0700 (PDT) MIME-Version: 1.0 References: <20240817062449.21164-1-21cnbao@gmail.com> <7050deab-e99c-4c83-b7b9-b5dad42f4e95@redhat.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Tue, 20 Aug 2024 09:48:36 +1200 Message-ID: Subject: Re: [PATCH v3 0/4] mm: clarify nofail memory allocation To: Linus Torvalds Cc: David Hildenbrand , akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, mhocko@suse.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: AD5E818001D X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: is5rttcf3a5b31cx57n4g3owwnu4thxx X-HE-Tag: 1724104132-904989 X-HE-Meta: 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 4sqImwef 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 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 Tue, Aug 20, 2024 at 7:33=E2=80=AFAM Linus Torvalds wrote: > > On Mon, 19 Aug 2024 at 12:23, Barry Song <21cnbao@gmail.com> wrote: > > > > > > That could be an exploit taking advantage of those improper callers, > > So? > > FIX THE BUGGY CODE. That's definitely in progress, with patch 1/4 addressing vdpa. There's also an RFC to enforce DIRECT_RECLAMATION for __GFP_NOFAIL, which will prevent passing unsupported flags to the memory management system: https://lore.kernel.org/all/20240724085544.299090-6-21cnbao@gmail.com/ > > Don't make insane and incorrect changes to the MM code and spread > Fear, Uncertainty and Doubt. > > > thus it wouldn=E2=80=99t necessarily result in an immediate oops in cal= lers but > > result in an exploit > > No. Any bug can be an exploit. Don't try to make this something > special by calling it an exploit. > > NULL pointer dereferences are some of the *least* worrisome bugs, > because we don't allow people to mmap the NULL area anyway. > > So just stop spreading FUD. We don't improve the kernel by making > excuses for bugs, we improve it by fixing things. > > And any caller that asks for NOFAIL with bad parameters is buggy. The > MM code should NOT try to fix it up, and dammit, BUG_ON() is not > acceptable as a debugging help. Never was, never will be. Okay, I see your point. However, the discussion originally began with just a simple WARN_ON() to flag improper usage: https://lore.kernel.org/linux-mm/20240717230025.77361-1-21cnbao@gmail.com/ Now, it seems we've come full circle and are opting to use WARN_ON_ONCE() instead? > > Worry-warts already do "reboot-on-warn". > > Linus Thanks Barry