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Fri, 12 Jul 2024 01:04:19 -0700 (PDT) Received: from google.com ([2401:fa00:8f:203:acec:d0e8:b0dd:8593]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70b438c0996sm6864562b3a.60.2024.07.12.01.04.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Jul 2024 01:04:18 -0700 (PDT) Date: Fri, 12 Jul 2024 17:04:14 +0900 From: Sergey Senozhatsky To: Pei Li , Andrew Morton , David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, syzkaller-bugs@googlegroups.com, linux-kernel-mentees@lists.linuxfoundation.org, syzbot+35a4414f6e247f515443@syzkaller.appspotmail.com Subject: Re: [PATCH] mm: Fix mmap_assert_locked() in follow_pte() Message-ID: <20240712080414.GA47643@google.com> References: <20240710-bug12-v1-1-0e5440f9b8d3@gmail.com> <92a2dc30-6e48-44ea-9cde-693b911f200d@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel-mentees@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <92a2dc30-6e48-44ea-9cde-693b911f200d@redhat.com> On (24/07/11 23:33), David Hildenbrand wrote: [..] > > @@ -1815,9 +1815,16 @@ static void unmap_single_vma(struct mmu_gather *tlb, > > if (vma->vm_file) > > uprobe_munmap(vma, start, end); > > - if (unlikely(vma->vm_flags & VM_PFNMAP)) > > + if (unlikely(vma->vm_flags & VM_PFNMAP)) { > > + if (!mm_wr_locked) > > + mmap_read_lock(vma->vm_mm); > > + > > untrack_pfn(vma, 0, 0, mm_wr_locked); > > + if (!mm_wr_locked) > > + mmap_read_unlock(vma->vm_mm); > > + } > > + > > if (start != end) { > > if (unlikely(is_vm_hugetlb_page(vma))) { > > I'm not sure if this is the right fix. I like to understand how we end up > without the mmap lock at least in read mode in that path? I suspect this is causing a deadlock: [ 10.263161] ============================================ [ 10.263165] WARNING: possible recursive locking detected [ 10.263170] 6.10.0-rc7-next-20240712+ #645 Tainted: G N [ 10.263177] -------------------------------------------- [ 10.263179] (direxec)/166 is trying to acquire lock: [ 10.263184] ffff88810b4f0198 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_lock+0x12/0x40 [ 10.263217] [ 10.263217] but task is already holding lock: [ 10.263219] ffff88810b4f0198 (&mm->mmap_lock){++++}-{3:3}, at: exit_mmap+0x9c/0x830 [ 10.263238] [ 10.263238] other info that might help us debug this: [ 10.263241] Possible unsafe locking scenario: [ 10.263241] [ 10.263243] CPU0 [ 10.263245] ---- [ 10.263247] lock(&mm->mmap_lock); [ 10.263252] lock(&mm->mmap_lock); [ 10.263257] [ 10.263257] *** DEADLOCK *** [ 10.263257] [ 10.263259] May be due to missing lock nesting notation [ 10.263259] [ 10.263262] 3 locks held by (direxec)/166: [ 10.263267] #0: ffff88810b4e8548 (&sig->cred_guard_mutex){+.+.}-{3:3}, at: bprm_execve+0x70/0x1110 [ 10.263286] #1: ffff88810b4e85e0 (&sig->exec_update_lock){+.+.}-{3:3}, at: exec_mmap+0x9f/0x510 [ 10.263302] #2: ffff88810b4f0198 (&mm->mmap_lock){++++}-{3:3}, at: exit_mmap+0x9c/0x830 [ 10.263318] [ 10.263318] stack backtrace: [ 10.263329] CPU: 6 UID: 0 PID: 166 Comm: (direxec) Tainted: G N 6.10.0-rc7-next-20240712+ #645 [ 10.263340] Tainted: [N]=TEST [ 10.263349] Call Trace: [ 10.263355] [ 10.263360] dump_stack_lvl+0xa3/0xeb [ 10.263375] print_deadlock_bug+0x4d5/0x680 [ 10.263387] __lock_acquire+0x65fb/0x7830 [ 10.263408] ? lock_is_held_type+0xdd/0x150 [ 10.263425] lock_acquire+0x14c/0x3e0 [ 10.263433] ? mmap_read_lock+0x12/0x40 [ 10.263445] ? lock_is_held_type+0xdd/0x150 [ 10.263454] down_read+0x58/0x9a0 [ 10.263461] ? mmap_read_lock+0x12/0x40 [ 10.263476] mmap_read_lock+0x12/0x40 [ 10.263485] unmap_single_vma+0x1bf/0x240 [ 10.263497] unmap_vmas+0x146/0x1c0 [ 10.263511] exit_mmap+0x13d/0x830 [ 10.263533] __mmput+0xc2/0x2c0 [ 10.263556] exec_mmap+0x4cb/0x510 [ 10.263580] begin_new_exec+0xfe6/0x1ba0 [ 10.263612] load_elf_binary+0x797/0x22a0 [ 10.263637] ? load_misc_binary+0x53a/0x930 [ 10.263656] ? lock_release+0x50f/0x830 [ 10.263673] ? bprm_execve+0x6d7/0x1110 [ 10.263693] bprm_execve+0x70d/0x1110 [ 10.263730] do_execveat_common+0x44b/0x600 [ 10.263745] __x64_sys_execve+0x8e/0xa0 [ 10.263754] do_syscall_64+0x71/0x110 [ 10.263764] entry_SYSCALL_64_after_hwframe+0x4b/0x53