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Message-ID: <CAJuCfpEcqAiK-z=EZ5im12F2wfGHYogiMHaTC4t5uopLmBKQPw@mail.gmail.com>
Date: Mon, 26 Jan 2026 09:20:43 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Hillf Danton <hdanton@...a.com>
Cc: syzbot <syzbot+4e70c8e0a2017b432f7a@...kaller.appspotmail.com>, axboe@...nel.dk,
linux-block@...r.kernel.org, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [block?] possible deadlock in blkdev_read_iter
On Sat, Jan 24, 2026 at 3:32 AM Hillf Danton <hdanton@...a.com> wrote:
>
> Add Lorenzo and Suren
Thanks!
>
> > Date: Fri, 23 Jan 2026 15:14:36 -0800
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: 24d479d26b25 Linux 6.19-rc6
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=100033fa580000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=1859476832863c41
> > dashboard link: https://syzkaller.appspot.com/bug?extid=4e70c8e0a2017b432f7a
> > compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11451b9a580000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1045e852580000
> >
> > Downloadable assets:
> > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-24d479d2.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/d0f3c47f6869/vmlinux-24d479d2.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/800231513703/bzImage-24d479d2.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+4e70c8e0a2017b432f7a@...kaller.appspotmail.com
> >
> > WARNING: possible circular locking dependency detected
> > syzkaller #0 Not tainted
> > ------------------------------------------------------
> > syz.0.17/6091 is trying to acquire lock:
> > ffff8881061287a8 (
> > &sb->s_type->i_mutex_key#8){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1042 [inline]
> > &sb->s_type->i_mutex_key#8){++++}-{4:4}, at: blkdev_read_iter+0x19e/0x500 block/fops.c:855
> >
> > but task is already holding lock:
> > ffff888012aa0448 (vm_lock){++++}-{0:0}, at: lock_next_vma+0x10e/0xed0 mm/mmap_lock.c:334
> >
> > which lock already depends on the new lock.
> >
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #2 (vm_lock){++++}-{0:0}:
> > __vma_enter_locked+0x260/0x770 mm/mmap_lock.c:72
> > __vma_start_write+0x21/0x160 mm/mmap_lock.c:104
> > vma_start_write include/linux/mmap_lock.h:213 [inline]
> > mprotect_fixup+0x4e3/0xb80 mm/mprotect.c:768
> > setup_arg_pages+0x4a2/0xbb0 fs/exec.c:670
> > load_elf_binary+0xb5b/0x4fe0 fs/binfmt_elf.c:1028
> > search_binary_handler fs/exec.c:1669 [inline]
> > exec_binprm fs/exec.c:1701 [inline]
> > bprm_execve fs/exec.c:1753 [inline]
> > bprm_execve+0x8c2/0x1620 fs/exec.c:1729
> > kernel_execve+0x2ef/0x3b0 fs/exec.c:1919
> > try_to_run_init_process init/main.c:1506 [inline]
> > kernel_init+0x14a/0x2b0 init/main.c:1634
> > ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
> > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
> >
> > -> #1 (&mm->mmap_lock){++++}-{4:4}:
> > __might_fault mm/memory.c:7174 [inline]
> > __might_fault+0x113/0x190 mm/memory.c:7168
> > _copy_to_iter+0x1c2/0x1710 lib/iov_iter.c:196
> > copy_page_to_iter lib/iov_iter.c:374 [inline]
> > copy_page_to_iter+0x12a/0x1e0 lib/iov_iter.c:361
> > copy_folio_to_iter include/linux/uio.h:204 [inline]
> > filemap_read+0x6b1/0xe40 mm/filemap.c:2851
> > blkdev_read_iter+0x1ac/0x500 block/fops.c:856
> > new_sync_read fs/read_write.c:491 [inline]
> > vfs_read+0x8bf/0xcf0 fs/read_write.c:572
> > ksys_read+0x12a/0x250 fs/read_write.c:715
> > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> > do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > -> #0 (&sb->s_type->i_mutex_key#8){++++}-{4:4}:
> > check_prev_add kernel/locking/lockdep.c:3165 [inline]
> > check_prevs_add kernel/locking/lockdep.c:3284 [inline]
> > validate_chain kernel/locking/lockdep.c:3908 [inline]
> > __lock_acquire+0x1669/0x2890 kernel/locking/lockdep.c:5237
> > lock_acquire kernel/locking/lockdep.c:5868 [inline]
> > lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
> > down_read+0x9b/0x460 kernel/locking/rwsem.c:1537
> > inode_lock_shared include/linux/fs.h:1042 [inline]
> > blkdev_read_iter+0x19e/0x500 block/fops.c:855
> > __kernel_read+0x3f3/0xbf0 fs/read_write.c:530
> > freader_fetch+0x1d7/0x9d0 lib/buildid.c:100
> > __build_id_parse.isra.0+0xdd/0x6c0 lib/buildid.c:297
> > do_procmap_query+0xb0e/0x1080 fs/proc/task_mmu.c:733
> > procfs_procmap_ioctl+0x9d/0xe0 fs/proc/task_mmu.c:813
> > vfs_ioctl fs/ioctl.c:51 [inline]
> > __do_sys_ioctl fs/ioctl.c:597 [inline]
> > __se_sys_ioctl fs/ioctl.c:583 [inline]
> > __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
> > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> > do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
It looks like:
#0 is executing PROCMAP_QUERY ioclt, read-locks vm_lock and then calls
build_id_parse()->__build_id_parse(...,
may_fault=true)->__kernel_read() which eventually takes
inode->i_rwsem.
#1 is a file-backed page fault which asserts that it might take
mmap_lock for read.
#2 is load_elf_binary()->mprotect_fixup() which write-locks both
mmap_lock and vm_lock. I'm guessing it already holds inode->i_rwsem
before write-locking these locks.
Originally I thought the issue is most liley introduced in
d9d1c2d81797 ("fs/proc/task_mmu: execute PROCMAP_QUERY ioctl under
per-vma locks"). But if #2 indeed takes inode->i_rwsem before
write-locking mmap_lock, then the problem should exist even before
that change when we didn't use vm_lock and relied on mmap_lock...
I'll try to analyze this more before attempting a fix.
> > other info that might help us debug this:
> >
> > Chain exists of:
> > &sb->s_type->i_mutex_key#8 --> &mm->mmap_lock --> vm_lock
> >
> > Possible unsafe locking scenario:
> >
> > CPU0 CPU1
> > ---- ----
> > rlock(vm_lock);
> > lock(&mm->mmap_lock);
> > lock(vm_lock);
> > rlock(&sb->s_type->i_mutex_key#8);
> >
> > *** DEADLOCK ***
> >
> > 1 lock held by syz.0.17/6091:
> > #0: ffff888012aa0448 (vm_lock){++++}-{0:0}, at: lock_next_vma+0x10e/0xed0 mm/mmap_lock.c:334
> >
> > stack backtrace:
> > CPU: 2 UID: 0 PID: 6091 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> > Call Trace:
> > <TASK>
> > __dump_stack lib/dump_stack.c:94 [inline]
> > dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
> > print_circular_bug+0x275/0x340 kernel/locking/lockdep.c:2043
> > check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
> > check_prev_add kernel/locking/lockdep.c:3165 [inline]
> > check_prevs_add kernel/locking/lockdep.c:3284 [inline]
> > validate_chain kernel/locking/lockdep.c:3908 [inline]
> > __lock_acquire+0x1669/0x2890 kernel/locking/lockdep.c:5237
> > lock_acquire kernel/locking/lockdep.c:5868 [inline]
> > lock_acquire+0x179/0x330 kernel/locking/lockdep.c:5825
> > down_read+0x9b/0x460 kernel/locking/rwsem.c:1537
> > inode_lock_shared include/linux/fs.h:1042 [inline]
> > blkdev_read_iter+0x19e/0x500 block/fops.c:855
> > __kernel_read+0x3f3/0xbf0 fs/read_write.c:530
> > freader_fetch+0x1d7/0x9d0 lib/buildid.c:100
> > __build_id_parse.isra.0+0xdd/0x6c0 lib/buildid.c:297
> > do_procmap_query+0xb0e/0x1080 fs/proc/task_mmu.c:733
> > procfs_procmap_ioctl+0x9d/0xe0 fs/proc/task_mmu.c:813
> > vfs_ioctl fs/ioctl.c:51 [inline]
> > __do_sys_ioctl fs/ioctl.c:597 [inline]
> > __se_sys_ioctl fs/ioctl.c:583 [inline]
> > __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
> > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> > do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > RIP: 0033:0x7ff1a238f7c9
> > Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007ffebbe538b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 00007ff1a25e5fa0 RCX: 00007ff1a238f7c9
> > RDX: 0000200000000180 RSI: 00000000c0686611 RDI: 0000000000000004
> > RBP: 00007ff1a2413f91 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > R13: 00007ff1a25e5fa0 R14: 00007ff1a25e5fa0 R15: 0000000000000003
> > </TASK>
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