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Message-ID: <CAJuCfpEJUeQcpfbh-0KTsp1UdTs5yrKTbvAV6QOKdQHJZ2HWww@mail.gmail.com>
Date: Mon, 26 Jan 2026 14:33:21 -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, Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [syzbot] [block?] possible deadlock in blkdev_read_iter
On Mon, Jan 26, 2026 at 9:20 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> 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.
I was able to reproduce the same issue even after reverting
d9d1c2d81797. The deadlock in this case is simpler and involves
mmap_lock instead of vm_lock (see below).
Looks like the race is between the read() syscall and do_procmap_query().
I'll continue investigating, in the meantime CC'ing Andrii.
[ 62.320932][ T9229]
[ 62.321471][ T9229] ======================================================
[ 62.323016][ T9229] WARNING: possible circular locking dependency detected
[ 62.324618][ T9229] 6.19.0-rc6-00001-g40bea6261b2a #42 Not tainted
[ 62.326013][ T9229] ------------------------------------------------------
[ 62.327560][ T9229] hillf/9229 is trying to acquire lock:
[ 62.328821][ T9229] ffff888145b7b5a8
(&sb->s_type->i_mutex_key#8){++++}-{4:4}, at:
blkdev_read_iter+0x2a7/0x4e0
[ 62.331102][ T9229]
[ 62.331102][ T9229] but task is already holding lock:
[ 62.332722][ T9229] ffff888183a6e540 (&mm->mmap_lock){++++}-{4:4},
at: do_procmap_query+0x39f/0x1050
[ 62.334795][ T9229]
[ 62.334795][ T9229] which lock already depends on the new lock.
[ 62.334795][ T9229]
[ 62.337072][ T9229]
[ 62.337072][ T9229] the existing dependency chain (in reverse order) is:
[ 62.338998][ T9229]
[ 62.338998][ T9229] -> #1 (&mm->mmap_lock){++++}-{4:4}:
[ 62.340646][ T9229] __might_fault+0xed/0x170
[ 62.341763][ T9229] _copy_to_iter+0x118/0x1720
[ 62.342913][ T9229] copy_page_to_iter+0x12d/0x1e0
[ 62.344167][ T9229] filemap_read+0x720/0x10a0
[ 62.345298][ T9229] blkdev_read_iter+0x2b5/0x4e0
[ 62.346480][ T9229] vfs_read+0x7f4/0xae0
[ 62.347518][ T9229] ksys_read+0x12a/0x250
[ 62.348584][ T9229] do_syscall_64+0xcb/0xf80
[ 62.349707][ T9229] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 62.351116][ T9229]
[ 62.351116][ T9229] -> #0 (&sb->s_type->i_mutex_key#8){++++}-{4:4}:
[ 62.353012][ T9229] __lock_acquire+0x1509/0x26d0
[ 62.354213][ T9229] lock_acquire+0x185/0x340
[ 62.355323][ T9229] down_read+0x98/0x490
[ 62.356441][ T9229] blkdev_read_iter+0x2a7/0x4e0
[ 62.357619][ T9229] __kernel_read+0x39a/0xa90
[ 62.358767][ T9229] freader_fetch+0x1d5/0xa80
[ 62.359927][ T9229] __build_id_parse.isra.0+0xea/0x6a0
[ 62.361232][ T9229] do_procmap_query+0xd75/0x1050
[ 62.362434][ T9229] procfs_procmap_ioctl+0x7a/0xb0
[ 62.363687][ T9229] __x64_sys_ioctl+0x18e/0x210
[ 62.364863][ T9229] do_syscall_64+0xcb/0xf80
[ 62.365977][ T9229] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 62.367394][ T9229]
[ 62.367394][ T9229] other info that might help us debug this:
[ 62.367394][ T9229]
[ 62.369637][ T9229] Possible unsafe locking scenario:
[ 62.369637][ T9229]
[ 62.371237][ T9229] CPU0 CPU1
[ 62.372441][ T9229] ---- ----
[ 62.373687][ T9229] rlock(&mm->mmap_lock);
[ 62.374688][ T9229]
lock(&sb->s_type->i_mutex_key#8);
[ 62.376444][ T9229] lock(&mm->mmap_lock);
[ 62.377956][ T9229] rlock(&sb->s_type->i_mutex_key#8);
[ 62.379165][ T9229]
[ 62.379165][ T9229] *** DEADLOCK ***
[ 62.379165][ T9229]
[ 62.380952][ T9229] 1 lock held by hillf/9229:
[ 62.381971][ T9229] #0: ffff888183a6e540
(&mm->mmap_lock){++++}-{4:4}, at: do_procmap_query+0x39f/0x1050
[ 62.384162][ T9229]
[ 62.384162][ T9229] stack backtrace:
[ 62.385458][ T9229] CPU: 3 UID: 0 PID: 9229 Comm: hillf Not tainted
6.19.0-rc6-00001-g40bea6261b2a #42 PREEMPT(full)
[ 62.385471][ T9229] Hardware name: QEMU Standard PC (i440FX + PIIX,
1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[ 62.385477][ T9229] Call Trace:
[ 62.385482][ T9229] <TASK>
[ 62.385487][ T9229] dump_stack_lvl+0x100/0x190
[ 62.385505][ T9229] print_circular_bug.cold+0x185/0x1d5
[ 62.385521][ T9229] check_noncircular+0x14a/0x170
[ 62.385534][ T9229] __lock_acquire+0x1509/0x26d0
[ 62.385547][ T9229] lock_acquire+0x185/0x340
[ 62.385557][ T9229] ? blkdev_read_iter+0x2a7/0x4e0
[ 62.385569][ T9229] ? __pfx___might_resched+0x10/0x10
[ 62.385583][ T9229] down_read+0x98/0x490
[ 62.385593][ T9229] ? blkdev_read_iter+0x2a7/0x4e0
[ 62.385603][ T9229] ? __pfx_down_read+0x10/0x10
[ 62.385612][ T9229] ? lock_acquire+0x185/0x340
[ 62.385622][ T9229] ? is_bpf_text_address+0x25/0x1a0
[ 62.385634][ T9229] blkdev_read_iter+0x2a7/0x4e0
[ 62.385645][ T9229] __kernel_read+0x39a/0xa90
[ 62.385658][ T9229] ? __pfx___kernel_read+0x10/0x10
[ 62.385671][ T9229] ? __lock_acquire+0x481/0x26d0
[ 62.385683][ T9229] freader_fetch+0x1d5/0xa80
[ 62.385697][ T9229] ? find_held_lock+0x2b/0x80
[ 62.385712][ T9229] ? __pfx_freader_fetch+0x10/0x10
[ 62.385725][ T9229] ? __asan_memset+0x27/0x50
[ 62.385737][ T9229] __build_id_parse.isra.0+0xea/0x6a0
[ 62.385751][ T9229] ? __pfx___build_id_parse.isra.0+0x10/0x10
[ 62.385766][ T9229] ? __pfx_find_vma+0x10/0x10
[ 62.385774][ T9229] ? __might_fault+0x129/0x170
[ 62.385788][ T9229] do_procmap_query+0xd75/0x1050
[ 62.385798][ T9229] ? __pfx_do_procmap_query+0x10/0x10
[ 62.385807][ T9229] ? __sanitizer_cov_trace_switch+0x53/0x90
[ 62.385817][ T9229] ? do_vfs_ioctl+0x226/0x13b0
[ 62.385828][ T9229] ? __pfx_do_vfs_ioctl+0x10/0x10
[ 62.385839][ T9229] ? putname+0xfc/0x1b0
[ 62.385846][ T9229] ? putname+0x101/0x1b0
[ 62.385857][ T9229] ? __x64_sys_openat+0x143/0x210
[ 62.385867][ T9229] procfs_procmap_ioctl+0x7a/0xb0
[ 62.385877][ T9229] ? __pfx_procfs_procmap_ioctl+0x10/0x10
[ 62.385888][ T9229] __x64_sys_ioctl+0x18e/0x210
[ 62.385899][ T9229] do_syscall_64+0xcb/0xf80
[ 62.385913][ T9229] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 62.385923][ T9229] RIP: 0033:0x412209
[ 62.385931][ T9229] Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f
44 00 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 d8 ff ff ff f7 d8
64 89 01 48
[ 62.385940][ T9229] RSP: 002b:00007fff380d5588 EFLAGS: 00000217
ORIG_RAX: 0000000000000010
[ 62.385950][ T9229] RAX: ffffffffffffffda RBX: 00007fff380d56c8
RCX: 0000000000412209
[ 62.385956][ T9229] RDX: 0000200000000180 RSI: 00000000c0686611
RDI: 0000000000000004
[ 62.385962][ T9229] RBP: 00007fff380d55a0 R08: 0000000000000000
R09: 00007fff380d5640
[ 62.385968][ T9229] R10: 0000000000000000 R11: 0000000000000217
R12: 00007fff380d56b8
[ 62.385974][ T9229] R13: 0000000000000002 R14: 00000000004a0e40
R15: 0000000000000002
[ 62.385982][ T9229] </TASK>
>
> > > 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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