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[2003:cb:c70e:6800:9933:28db:f83a:ef5]) by smtp.gmail.com with ESMTPSA id u16-20020adfdb90000000b003175a994555sm17817887wri.6.2023.08.09.11.04.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Aug 2023 11:04:06 -0700 (PDT) Message-ID: <0ab6524a-6917-efe2-de69-f07fb5cdd9d2@redhat.com> Date: Wed, 9 Aug 2023 20:04:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v7 0/6] Per-VMA lock support for swap and userfaults To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, willy@infradead.org, hannes@cmpxchg.org, mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz, minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com, lstoakes@gmail.com, hdanton@sina.com, apopple@nvidia.com, peterx@redhat.com, ying.huang@intel.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, pasha.tatashin@soleen.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com References: <20230630211957.1341547-1-surenb@google.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: DE28A40026 X-Stat-Signature: 4ii8nbcz1zefse1zt8d6yei4u8f9ph8t X-Rspam-User: X-HE-Tag: 1691604250-727519 X-HE-Meta: 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 fNrdndK0 TWGXggYpkZviuTNBf8E/64R56WdEda4xnXzZi3pa/qbli4PFthyPpdxRjXjRp7rf8d6Q+q/70AH27D/yDWuujzOtO/eYqvmryCY51ZcMyRsPpZR7+tyor4f2MS6Hg1TtF7H9OLXkFq3KakQ8hAsR/JFDnc7WTadI4Lw5Wv5JZiV9v3nkPdBLMoKrGdugASVBCb3z2OoYkoUy5Tqdziw6ZGscvCAOyULVhTpyvhQbR4t2I70pG6+2pE7Z2qTadzmPsybQji3LqY8g2MVdV0v4WZrVqo7C8qAFFX/b+5Lv2/lG1uvkeWUzNt3zQ16tnqzLM23DzASq90SR3ZYNHeqnvG5WHwqipJjKLHg9/6yrO5qw0M7RhuFX9dGFmS4HoEXGY6GQe X-Bogosity: Ham, tests=bogofilter, spamicity=0.000348, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: >>>> Which ends up being >>>> >>>> VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); >>>> >>>> I did not check if this is also the case on mainline, and if this series is responsible. >>> >>> Thanks for reporting! I'm checking it now. >> >> Hmm. From the code it's not obvious how lock_mm_and_find_vma() ends up >> calling find_vma() without mmap_lock after successfully completing >> get_mmap_lock_carefully(). lock_mm_and_find_vma+0x3f/0x270 points to >> the first invocation of find_vma(), so this is not even the lock >> upgrade path... I'll try to reproduce this issue and dig up more but >> from the information I have so far this issue does not seem to be >> related to this series. I just checked on mainline and it does not fail there. > > This is really weird. I added mmap_assert_locked(mm) calls into > get_mmap_lock_carefully() right after we acquire mmap_lock read lock > and one of them triggers right after successful > mmap_read_lock_killable(). Here is my modified version of > get_mmap_lock_carefully(): > > static inline bool get_mmap_lock_carefully(struct mm_struct *mm, > struct pt_regs *regs) { > /* Even if this succeeds, make it clear we might have slept */ > if (likely(mmap_read_trylock(mm))) { > might_sleep(); > mmap_assert_locked(mm); > return true; > } > if (regs && !user_mode(regs)) { > unsigned long ip = instruction_pointer(regs); > if (!search_exception_tables(ip)) > return false; > } > if (!mmap_read_lock_killable(mm)) { > mmap_assert_locked(mm); <---- generates a BUG > return true; > } > return false; > } Ehm, that's indeed weird. > > AFAIKT conditions for mmap_read_trylock() and > mmap_read_lock_killable() are checked correctly. Am I missing > something? Weirdly enough, it only triggers during that specific uffd test, right? -- Cheers, David / dhildenb