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Howlett" , Lorenzo Stoakes , David Hildenbrand , Jann Horn , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Colin Cross Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250624-anon_name_cleanup-v2-0-600075462a11@suse.cz> <20250624-anon_name_cleanup-v2-1-600075462a11@suse.cz> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <20250624-anon_name_cleanup-v2-1-600075462a11@suse.cz> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 9F4421A001F X-Stat-Signature: j1roaouk8byniujnhpn9a13khor19taj X-Rspam-User: X-HE-Tag: 1750784507-280802 X-HE-Meta: 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 pqyNpl7O LZfoECdlQq/kXIkT6C77+sIqjetWwnpyPdEw8IaTqwFj9vkrFHCnWBlfQQ34mHJwqdyXk/UxDDrVjuNnFK4WuaSlMtO2PuaIffJ/wtVKY9dZTtPQns8u/5FJCI/fPHuQUlS9kgNm0VK6qcn8dh58e2TyBHlBdwSjpStdVYVExH6i0NS+oVV29wmUuaMWjOntj3FVw1xV9fybyEIX/f0yZIioQxK98aHAMRnorD5ny5h/p5MFYWpIqdS6RtaYJZ2k9hUgZyrSJl0mhbU8I6dcoqLw4Zmy1GI4z08KdA9gQ7jTsnk4/aJXWEJhH+etrF7ZsSVtXwBuWPFoKlGK7S30BzPNXKMUXZ5Z4ERFbKsAp/Ua2KMcVRru0qZ9+PIy37AxHPCak5NZZ3Wq5u8BJtaJbiAQ76XQ22BsD5MgC2ReI9/jQzfj+qzdIER0KeOrZyhuQY8hysIn4a2+WILduvPAKAQcEZs1dBCiFkmy5udE46ZVDl9ROpso1vLxtNUwI7RRoJZsmpD+skuD9B6tEndcsgksgDIpY7DTysU4RyEdPtHAUZ7UobaYXQopAn2PAs54FZHvHSKgvU5G3DFiG2Mcqkx5fr4U7OtHjH4OGe4i/0dpAA/zngoIzsjwI4DlgdEPg/jMqtMvXUhx9/mXeRpFtGuLc1k8U/ZxTa/tcHbo5+SwlGXAoyd8jPt8cVSiuOW1islg6obPRId3MMIbHGriW5eCDsgFIxWr/Pkmx1ssitaGaHLY= 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 6/24/25 15:03, Vlastimil Babka wrote: > Since the introduction in 9a10064f5625 ("mm: add a field to store names > for private anonymous memory") the code to set anon_name on a vma has > been using madvise_update_vma() to call replace_anon_vma_name(). Since > the former is called also by a number of other madvise behaviours that > do not set a new anon_name, they have been passing the existing > anon_name of the vma to make replace_vma_anon_name() a no-op. > > This is rather wasteful as it needs anon_vma_name_eq() to determine the > no-op situations, and checks for when replace_vma_anon_name() is allowed > (the vma is anon/shmem) duplicate the checks already done earlier in > madvise_vma_behavior(). It has also lead to commit 942341dcc574 ("mm: > fix use-after-free when anon vma name is used after vma is freed") > adding anon_name refcount get/put operations exactly to the cases that > actually do not change anon_name - just so the replace_vma_anon_name() > can keep safely determining it has nothing to do. > > The recent madvise cleanups made this suboptimal handling very obvious, > but happily also allow for an easy fix. madvise_update_vma() now has the > complete information whether it's been called to set a new anon_name, so > stop passing it the existing vma's name and doing the refcount get/put > in its only caller madvise_vma_behavior(). > > In madvise_update_vma() itself, limit calling of replace_anon_vma_name() > only to cases where we are setting a new name, otherwise we know it's a > no-op. We can rely solely on the __MADV_SET_ANON_VMA_NAME behaviour and > can remove the duplicate checks for vma being anon/shmem that were done > already in madvise_vma_behavior(). > > Additionally, by using vma_modify_flags() when not modifying the > anon_name, avoid explicitly passing the existing vma's anon_name and > storing a pointer to it in struct madv_behavior or a local variable. > This prevents the danger of accessing a freed anon_name after vma > merging, previously fixed by commit 942341dcc574. > > Signed-off-by: Vlastimil Babka With fixed up function names as pointed out by Suren: Since the introduction in 9a10064f5625 ("mm: add a field to store names for private anonymous memory") the code to set anon_name on a vma has been using madvise_update_vma() to call replace_anon_vma_name(). Since the former is called also by a number of other madvise behaviours that do not set a new anon_name, they have been passing the existing anon_name of the vma to make replace_anon_vma_name() a no-op. This is rather wasteful as it needs anon_vma_name_eq() to determine the no-op situations, and checks for when replace_anon_vma_name() is allowed (the vma is anon/shmem) duplicate the checks already done earlier in madvise_vma_behavior(). It has also lead to commit 942341dcc574 ("mm: fix use-after-free when anon vma name is used after vma is freed") adding anon_name refcount get/put operations exactly to the cases that actually do not change anon_name - just so the replace_anon_vma_name() can keep safely determining it has nothing to do. The recent madvise cleanups made this suboptimal handling very obvious, but happily also allow for an easy fix. madvise_update_vma() now has the complete information whether it's been called to set a new anon_name, so stop passing it the existing vma's name and doing the refcount get/put in its only caller madvise_vma_behavior(). In madvise_update_vma() itself, limit calling of replace_anon_vma_name() only to cases where we are setting a new name, otherwise we know it's a no-op. We can rely solely on the __MADV_SET_ANON_VMA_NAME behaviour and can remove the duplicate checks for vma being anon/shmem that were done already in madvise_vma_behavior(). Additionally, by using vma_modify_flags() when not modifying the anon_name, avoid explicitly passing the existing vma's anon_name and storing a pointer to it in struct madv_behavior or a local variable. This prevents the danger of accessing a freed anon_name after vma merging, previously fixed by commit 942341dcc574. Signed-off-by: Vlastimil Babka