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Fri, 9 Aug 2024 14:25:53 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id g1NHOvEmtmahEgAAD6G6ig (envelope-from ); Fri, 09 Aug 2024 14:25:53 +0000 Message-ID: <46d631a3-47f6-4ea7-9a69-32bf1a3adf01@suse.cz> Date: Fri, 9 Aug 2024 16:25:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 10/10] mm: rework vm_ops->close() handling on VMA merge Content-Language: en-US To: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: "Liam R . Howlett" References: <0afd85543d46fd743c0c71b6f6520f9580174b4f.1722849860.git.lorenzo.stoakes@oracle.com> 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+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <0afd85543d46fd743c0c71b6f6520f9580174b4f.1722849860.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D10AE40019 X-Stat-Signature: kuoyf4prdieqmutdoc1srtwk79cid58u X-HE-Tag: 1723213555-822313 X-HE-Meta: U2FsdGVkX19Wsmh5aUgiaa2Zf+cCIljRiisDeyeMcAuovycbMhr3JhA+l3zzVXHrYcL0PPq8bIuFSUquwd009F+SINNO4XwTBJzwqv+uLyz/6QH12Ni8StZ20peeec6Kl91Jml7TxQgPwtFAUs8RrINbKtxTv+4SoyZdf+3PA62+TOvwrFhs2nAB679iNSZCVFtiX4KKSNVGRPoX3aX86D4HVWVPAmKq2gBXRJpJXKMpvbwufNewh0OHfUsy9/0l6+5HtoRiIFshFK9IEQhLooK1rTxO9KeosIc7P6QP8fDH/BBAlHBGYAV70HKIB5t5VcNM/yW036oX0TGFBJJvYSzrnxKfNNPkvHcNKBOZupoSpFit/SS8X9bTZ0F7fIWns8auES8WRHFs+DfkNjDpv0Fw9t/fYm3Fj0HDbIsPNZ3TzvQIGrf1C5bOWf3IuHtGuZTUeb68+etwt589VMpJZmcX8SAZoTr79XNzfIV077cpXd5IrGSY+fThLO0cBW2MalNIryqziiFGAaSMKEccKDdytKyZyRpX51i8BQ4NNOPvel4vzjfLI6dCWoYSAlzi7eZzi5tuV6pOxGtkjb0uXglogyO3ObQBExy8Wl9OLFNNJAgzOEj8//F+htIECFRM0QTkIl7uHC8wjEUMuMphKm9fbRHuc/FEONhKx/tzyMc7S6IwAmMyJWVg+jrYmKC9umnGc/9jf/HOfj8KzzcaAubWWbzG7j8gBvOzjOGeJKW5wxu7FDPIGwrNFV6v7ymkSDHDzTJvbkYRovpYs9C9BdbaRAiBzGLsS/Ith8adtnQ/5QXyTufftgKFO4Z1EoLXPrgrthDn7c8gIAB7xI0SoexDnZE4u8gW4nfp6emZtvsa2g10pGRzOFwWMGrDbIQefQL70MvhNwSEhmO6pUNtwSSGd5qUvhsCLHFX1FgutVmzOmnLtD4RneTse3xhI6mLH2T+Y0OAA9AmbTgSSXH WYiRsddc 19X+4nzXR1m5hIs0hMWiTkXxTWJtoLylU1i5HP2iz4taPPUTrrh4VPCzCg5P5rFF8i6jlN9H2d2dLBe5erwiFz18JGym5lCtuhSzKjqPg6bMJkHAiBL7vKEBTFEwk+Kse1HPqbAqM6xGHcZARUAuV69O6wCT7yipnOiyJTsmlJUicmcMFsA5j7vRkJohdSWYEuOAKQM4/blGhUkU46mEI4W2+lpANueGhNxLrwVUa0gkmGWsFt1/3umbU0jVe2zkj/5NGx3ngmDsDY2vg5E36+eaknN5lUyRYYXA6Ptzf/alOHXNdXT+MJ+ru5/XxJt1kePrEWuQQiY4dlYk= 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 8/5/24 14:13, Lorenzo Stoakes wrote: > In commit 714965ca8252 ("mm/mmap: start distinguishing if vma can be > removed in mergeability test") we relaxed the VMA merge rules for VMAs > possessing a vm_ops->close() hook, permitting this operation in instances > where we wouldn't delete the VMA as part of the merge operation. > > This was later corrected in commit fc0c8f9089c2 ("mm, mmap: fix vma_merge() > case 7 with vma_ops->close") to account for a subtle case that the previous > commit had not taken into account. > > In both instances, we first rely on is_mergeable_vma() to determine whether > we might be dealing with a VMA that might be removed, taking advantage of > the fact that a 'previous' VMA will never be deleted, only VMAs that follow > it. > > The second patch corrects the instance where a merge of the previous VMA > into a subsequent one did not correctly check whether the subsequent VMA > had a vm_ops->close() handler. > > Both changes prevent merge cases that are actually permissible (for > instance a merge of a VMA into a following VMA with a vm_ops->close(), but > with no previous VMA, which would result in the next VMA being extended, > not deleted). > > In addition, both changes fail to consider the case where a VMA that would > otherwise be merged with the previous and next VMA might have > vm_ops->close(), on the assumption that for this to be the case, all three > would have to have the same vma->vm_file to be mergeable and thus the same > vm_ops. > > And in addition both changes operate at 50,000 feet, trying to guess > whether a VMA will be deleted. > > As we have majorly refactored the VMA merge operation and de-duplicated > code to the point where we know precisely where deletions will occur, this > patch removes the aforementioned checks altogether and instead explicitly > checks whether a VMA will be deleted. > > In cases where a reduced merge is still possible (where we merge both > previous and next VMA but the next VMA has a vm_ops->close hook, meaning we > could just merge the previous and current VMA), we do so, otherwise the > merge is not permitted. > > We take advantage of our userland testing to assert that this functions > correctly - replacing the previous limited vm_ops->close() tests with tests > for every single case where we delete a VMA. > > We also update all testing for both new and modified VMAs to set > vma->vm_ops->close() in every single instance where this would not prevent > the merge, to assert that we never do so. > > Signed-off-by: Lorenzo Stoakes Amazing! Acked-by: Vlastimil Babka > @@ -710,9 +706,30 @@ static struct vm_area_struct *vma_merge_modified(struct vma_merge_struct *vmg) > > /* If we span the entire VMA, a merge implies it will be deleted. */ > merge_will_delete_vma = left_side && right_side; > - /* If we merge both VMAs, then next is also deleted. */ Nit: This comment ... > + > + /* > + * If we need to remove vma in its entirety but are unable to do so, > + * we have no sensible recourse but to abort the merge. > + */ > + if (merge_will_delete_vma && !can_merge_remove_vma(vma)) > + return NULL; > + > + /* > + * If we merge both VMAs, then next is also deleted. This implies > + * merge_will_delete_vma also. > + */ ... changed to this comment. Seems spurious, could have been like that before already? I don't see how the new "This implies" part became relevant now? We already tested merge_will_delete_vma above. > merge_will_delete_next = merge_both; > > + /* > + * If we cannot delete next, then we can reduce the operation to merging > + * prev and vma (thereby deleting vma). > + */ > + if (merge_will_delete_next && !can_merge_remove_vma(next)) { > + merge_will_delete_next = false; > + merge_right = false; > + merge_both = false; > + } > + > /* No matter what happens, we will be adjusting vma. */ > vma_start_write(vma); >