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[109.81.94.157]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-59b268a28e8sm7969794a12.63.2024.07.18.00.12.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Jul 2024 00:12:38 -0700 (PDT) Date: Thu, 18 Jul 2024 09:12:37 +0200 From: Michal Hocko To: Christoph Hellwig Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, Barry Song , Uladzislau Rezki , Lorenzo Stoakes , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com> Subject: Re: [PATCH RFC] mm: warn potential return NULL for kmalloc_array and kvmalloc_array with __GFP_NOFAIL Message-ID: References: <20240717230025.77361-1-21cnbao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 093D880003 X-Stat-Signature: ytnh3c9rno1der3747j1ewnzuts755ku X-Rspam-User: X-HE-Tag: 1721286759-688508 X-HE-Meta: U2FsdGVkX19HR0CbxhOxhwnY0h0Cdx2JbI1LsLpCfVDnNlWrZXIMIYSxjta+gwNmIzrMw7p1Y4WxTZKFQQ2dtPTD5MK+mYK07lDoO/NOPmGVVwfeX4QGyB+pHpxQ5VMnsnhdsauBiEVzIOSSgYHAf4B+UP/S1IkyibmZ7aFx9lOYBWc04jyV9vUKtyGHsbhFQsBXAs+w4Irk6a7pY8dVwVVPEAeK+jYDYVUfG8Bya07UuB/jM1MXM+2KWB0MhNDLiS+ZljHy+NUFxcyf03t4npcP4yizknxf0/4yV0Vm0lUgWjUG0M1qtRhyEcVXVwd7zayqTyhQp1CCRu/5B6m0xS1KNKkzgKUP4A4RfSjDNdnUsPZHJDaNzd9y1OhQBgK7nMhAjU9yaVAxm8uKuC276lyTP/sZbHwnNkJbt1/Q2csBs0r6i0J8IlMysMrPkjdGKGutGqIH/lOWhPec6by1/ktKxya9v1+yMEKuMzeyTX0mQUgGEYbb89ZmjZ0ww0n5hZrO6u20T9PWqwjA9Hzmb7Kr3tvcaePqiqebJ0Bw7gHNfhI3J7UwlKbrOlhpnxDXl0aO09XknJHQE2Gv6y4uid/+SAOUWMm9XCJ/mYkTkOkMSSGEWj2Q4egZ8q5BKBU2wOYDzFc8Dt5yWc6Bs57iFkY5Sah00378dPfXu1nQkoLnDilEHGGFmLZ3gFEYlDkYwSVqJVvhafrFsjvW0tmOQ9KZ53Da1QzFJrxT/BskBSdfYBJnf7NfDTL3SivFiXMXic68jMUvbXFptx+plYeTnKocbYXw8qlvrikgTRrvtNO+g6CzzkJfBD6zA4Hh3J36QaBj1MVSxF8s0Gc/KBma3Jrm4flPhl0QiOmlNyAjTI4GRM2MNWzkMyGQlr5Rt06Ydw/eWR4uDmZxvfbQz7g71YeTYFavomy59wtLKLeVHzE7V8WL6KW2c1hsLX6QC4jvr05Aw7BVfpzU3ANeBzd aDjsgJGa lgdIW0YEwcQBfCLUFf4eU63MImVasSkrLGJfRLsgMA1Dx++mqgtnOvzRcZG+c52by/v9n/dEjpjMaqPSQf5lQg/EsSXKtPiCLMHZY5fKu5k6t9S7SDrl39DaSpgkARQzTeyxueCiVwi6Bd8qrLxiw7Rb+q/vil2pHhEhRmYOeMnIHvPbZOHQH1tgc1EwvFdyoaHZj3HYc9nWTqvctdsBwEcBkztwGViSH1wzzBeojKFkALCGUP9AHYC8u3kDqOR9p7a7IV9S0n4p7KsWRLEopioKiFMbDjsQexrACyA2bv6cgN5gF+MucHVdTKmW0JUiH0H1fN/qbypwBmErLj3V5efqXBxIDAOktjb4YRv8kJsQ1yzMbij2V+tBvSc4X3g879jcmjGs8FDbEBbihxW2FVzagIg== 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 Thu 18-07-24 00:04:54, Christoph Hellwig wrote: > On Thu, Jul 18, 2024 at 08:58:44AM +0200, Michal Hocko wrote: > > WARN_ON is effectively BUG_ON with panic_on_warn so if this happens to > > be in a user triggerable path then you would have an easy way to panic > > the whole machine. It is likely true that the kernel could oops just > > right after the failure but that could be recoverable at least. > > If you set panic_on_warn you are either debugging in which case it's > the right thing, or you are fucked. So don't do it unless you > expet frequent crashes. I do agree and I wouldn't recommend running panic_on_warn on anything even touching production setups. Reality check disagrees. > > If anything I would just pr_warn with caller address or add dump_stack > > to capture the full trace. That would give us the caller that needs > > fixing without panicing the system with panic_on_warn. > > The whole freaking point of __GFP_NOFAIL is that callers don't handle > allocation failures. So in fact a straight BUG is the right thing > here. OOPs from the NULL ptr could be just a safer option bacause it could be recoverable. Anyway, I am questioning that WARN/BUG/pr_warn on overflow check is adding any actual value because GFP_NOFAIL large allocations could be even more dangerous essentially rendering the system completely unsuabale. -- Michal Hocko SUSE Labs