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Tue, 24 Jun 2025 16:42:24 +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 eW51OHDVWmg4IwAAD6G6ig (envelope-from ); Tue, 24 Jun 2025 16:42:24 +0000 Message-ID: <992cff93-9ac9-40f9-a104-d9de0f3b8ef7@suse.cz> Date: Tue, 24 Jun 2025 18:42:24 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] mm, madvise: simplify anon_name handling Content-Language: en-US To: Lorenzo Stoakes Cc: Andrew Morton , "Liam R. Howlett" , David Hildenbrand , Jann Horn , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Colin Cross , 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> <60186e91-bf02-4d39-b745-ffb4e62632cb@lucifer.local> 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: <60186e91-bf02-4d39-b745-ffb4e62632cb@lucifer.local> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Flag: NO X-Spam-Score: -4.30 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[11]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:mid,suse.cz:email,oracle.com:email] X-Spam-Level: On 6/24/25 17:26, Lorenzo Stoakes wrote: > On Tue, Jun 24, 2025 at 03:03:45PM +0200, 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 > > Cheers, LGTM so: > > Reviewed-by: Lorenzo Stoakes > > I made sure to do some stress-ng --madvise testing with this series (+ my recent > fix) applied :P all good. Thanks for that! >> --- >> mm/madvise.c | 37 +++++++++++++------------------------ >> 1 file changed, 13 insertions(+), 24 deletions(-) >> >> diff --git a/mm/madvise.c b/mm/madvise.c >> index 4491bf080f55d6d1aeffb2ff0b8fdd28904af950..fca0e9b3e844ad766e83ac04cc0d7f4099c74005 100644 >> --- a/mm/madvise.c >> +++ b/mm/madvise.c >> @@ -176,25 +176,29 @@ static int replace_anon_vma_name(struct vm_area_struct *vma, >> } >> #endif /* CONFIG_ANON_VMA_NAME */ >> /* >> - * Update the vm_flags on region of a vma, splitting it or merging it as >> - * necessary. Must be called with mmap_lock held for writing; >> - * Caller should ensure anon_name stability by raising its refcount even when >> - * anon_name belongs to a valid vma because this function might free that vma. >> + * Update the vm_flags and/or anon_name on region of a vma, splitting it or >> + * merging it as necessary. Must be called with mmap_lock held for writing. >> */ >> static int madvise_update_vma(vm_flags_t new_flags, >> struct madvise_behavior *madv_behavior) >> { >> - int error; >> struct vm_area_struct *vma = madv_behavior->vma; >> struct madvise_behavior_range *range = &madv_behavior->range; >> struct anon_vma_name *anon_name = madv_behavior->anon_name; >> + bool set_new_anon_name = madv_behavior->behavior == __MADV_SET_ANON_VMA_NAME; >> VMA_ITERATOR(vmi, madv_behavior->mm, range->start); >> >> - if (new_flags == vma->vm_flags && anon_vma_name_eq(anon_vma_name(vma), anon_name)) >> + if (new_flags == vma->vm_flags && (!set_new_anon_name || >> + anon_vma_name_eq(anon_vma_name(vma), anon_name))) >> return 0; >> >> - vma = vma_modify_flags_name(&vmi, madv_behavior->prev, vma, >> + if (set_new_anon_name) >> + vma = vma_modify_flags_name(&vmi, madv_behavior->prev, vma, >> range->start, range->end, new_flags, anon_name); > > I will do a follow up (doesn't really belong here I'd say as involves change to > modify code) that makes this vma_modify_name() or vma_modify_anon_name() as this > is the only caller and we don't care about flags here :) Oh right, good idea!