[syzbot] [mm?] possible deadlock in __mmap_lock_do_trace_start_locking

[syzbot] [mm?] possible deadlock in __mmap_lock_do_trace_start_locking

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    443574b03387 riscv, bpf: Fix kfunc parameters incompatibil..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=13601320980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6fb1be60a193d440
dashboard link: https://syzkaller.appspot.com/bug?extid=6ff90931779bcdfc840c
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3f355021a085/disk-443574b0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/44cf4de7472a/vmlinux-443574b0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a99a36c7ad65/bzImage-443574b0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6ff90931779bcdfc840c@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.8.0-syzkaller-05236-g443574b03387 #0 Not tainted
------------------------------------------------------
syz-executor.2/5452 is trying to acquire lock:
ffff8880b9538528 (lock#10){+.+.}-{2:2}, at: local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
ffff8880b9538528 (lock#10){+.+.}-{2:2}, at: __mmap_lock_do_trace_start_locking+0x83/0x5f0 mm/mmap_lock.c:230

but task is already holding lock:
ffff8880b953e158 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:559

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&rq->__lock){-.-.}-{2:2}:
       lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
       _raw_spin_lock_nested+0x31/0x40 kernel/locking/spinlock.c:378
       raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:559
       raw_spin_rq_lock kernel/sched/sched.h:1385 [inline]
       rq_lock kernel/sched/sched.h:1699 [inline]
       task_fork_fair+0x61/0x1e0 kernel/sched/fair.c:12629
       sched_cgroup_fork+0x37c/0x410 kernel/sched/core.c:4845
       copy_process+0x2217/0x3df0 kernel/fork.c:2498
       kernel_clone+0x21e/0x8d0 kernel/fork.c:2796
       user_mode_thread+0x132/0x1a0 kernel/fork.c:2874
       rest_init+0x27/0x300 init/main.c:695
       arch_call_rest_init+0xe/0x10 init/main.c:831
       start_kernel+0x47a/0x500 init/main.c:1077
       x86_64_start_reservations+0x2a/0x30 arch/x86/kernel/head64.c:509
       x86_64_start_kernel+0x99/0xa0 arch/x86/kernel/head64.c:490
       common_startup_64+0x13e/0x147

-> #1 (&p->pi_lock){-.-.}-{2:2}:
       lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
       class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:553 [inline]
       try_to_wake_up+0xb0/0x1470 kernel/sched/core.c:4262
       rcu_read_unlock_special+0x3db/0x550 kernel/rcu/tree_plugin.h:655
       __rcu_read_unlock+0xa1/0x110 kernel/rcu/tree_plugin.h:426
       rcu_read_unlock include/linux/rcupdate.h:782 [inline]
       get_mem_cgroup_from_mm+0x1a3/0x2a0 mm/memcontrol.c:1112
       get_mm_memcg_path+0x1b/0x600 mm/mmap_lock.c:202
       __mmap_lock_do_trace_start_locking+0x134/0x5f0 mm/mmap_lock.c:230
       __mmap_lock_trace_start_locking include/linux/mmap_lock.h:29 [inline]
       mmap_read_trylock include/linux/mmap_lock.h:164 [inline]
       get_mmap_lock_carefully mm/memory.c:5497 [inline]
       lock_mm_and_find_vma+0x1f1/0x2f0 mm/memory.c:5557
       do_user_addr_fault arch/x86/mm/fault.c:1385 [inline]
       handle_page_fault arch/x86/mm/fault.c:1505 [inline]
       exc_page_fault+0x1a9/0x890 arch/x86/mm/fault.c:1563
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
       rep_movs_alternative+0x4a/0x70 arch/x86/lib/copy_user_64.S:65
       copy_user_generic arch/x86/include/asm/uaccess_64.h:110 [inline]
       raw_copy_from_user arch/x86/include/asm/uaccess_64.h:125 [inline]
       copy_from_user_iter lib/iov_iter.c:55 [inline]
       iterate_ubuf include/linux/iov_iter.h:29 [inline]
       iterate_and_advance2 include/linux/iov_iter.h:245 [inline]
       iterate_and_advance include/linux/iov_iter.h:271 [inline]
       __copy_from_iter lib/iov_iter.c:249 [inline]
       _copy_from_iter+0x257/0x1cf0 lib/iov_iter.c:260
       copy_from_iter include/linux/uio.h:204 [inline]
       copy_from_iter_full include/linux/uio.h:211 [inline]
       skb_do_copy_data_nocache include/net/sock.h:2231 [inline]
       skb_copy_to_page_nocache include/net/sock.h:2257 [inline]
       kcm_sendmsg+0xcca/0x27c0 net/kcm/kcmsock.c:858
       sock_sendmsg_nosec net/socket.c:730 [inline]
       __sock_sendmsg+0x221/0x270 net/socket.c:745
       sock_write_iter+0x2dd/0x400 net/socket.c:1160
       call_write_iter include/linux/fs.h:2108 [inline]
       new_sync_write fs/read_write.c:497 [inline]
       vfs_write+0xa84/0xcb0 fs/read_write.c:590
       ksys_write+0x1a0/0x2c0 fs/read_write.c:643
       do_syscall_64+0xfb/0x240
       entry_SYSCALL_64_after_hwframe+0x6d/0x75

-> #0 (lock#10){+.+.}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
       __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
       lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
       local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
       __mmap_lock_do_trace_start_locking+0x9c/0x5f0 mm/mmap_lock.c:230
       __mmap_lock_trace_start_locking include/linux/mmap_lock.h:29 [inline]
       mmap_read_trylock include/linux/mmap_lock.h:164 [inline]
       stack_map_get_build_id_offset+0x98d/0x9d0 kernel/bpf/stackmap.c:141
       __bpf_get_stack+0x4ad/0x5a0 kernel/bpf/stackmap.c:449
       ____bpf_get_stack_raw_tp kernel/trace/bpf_trace.c:1985 [inline]
       bpf_get_stack_raw_tp+0x1a3/0x240 kernel/trace/bpf_trace.c:1975
       bpf_prog_5c8cb7646b59f521+0x42/0x46
       bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
       __bpf_prog_run include/linux/filter.h:657 [inline]
       bpf_prog_run include/linux/filter.h:664 [inline]
       __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
       bpf_trace_run2+0x204/0x420 kernel/trace/bpf_trace.c:2420
       trace_tlb_flush+0xfa/0x120 include/trace/events/tlb.h:38
       switch_mm_irqs_off+0x7cb/0xae0
       context_switch kernel/sched/core.c:5393 [inline]
       __schedule+0x1054/0x4a20 kernel/sched/core.c:6736
       __schedule_loop kernel/sched/core.c:6813 [inline]
       schedule+0x14b/0x320 kernel/sched/core.c:6828
       exit_to_user_mode_loop kernel/entry/common.c:96 [inline]
       exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
       irqentry_exit_to_user_mode+0xe7/0x270 kernel/entry/common.c:225
       asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

other info that might help us debug this:

Chain exists of:
  lock#10 --> &p->pi_lock --> &rq->__lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&rq->__lock);
                               lock(&p->pi_lock);
                               lock(&rq->__lock);
  lock(lock#10);

 *** DEADLOCK ***

2 locks held by syz-executor.2/5452:
 #0: ffff8880b953e158 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:559
 #1: ffffffff8e131920 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:298 [inline]
 #1: ffffffff8e131920 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:750 [inline]
 #1: ffffffff8e131920 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2380 [inline]
 #1: ffffffff8e131920 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x114/0x420 kernel/trace/bpf_trace.c:2420

stack backtrace:
CPU: 1 PID: 5452 Comm: syz-executor.2 Not tainted 6.8.0-syzkaller-05236-g443574b03387 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e7/0x2e0 lib/dump_stack.c:106
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
 __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
 local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
 __mmap_lock_do_trace_start_locking+0x9c/0x5f0 mm/mmap_lock.c:230
 __mmap_lock_trace_start_locking include/linux/mmap_lock.h:29 [inline]
 mmap_read_trylock include/linux/mmap_lock.h:164 [inline]
 stack_map_get_build_id_offset+0x98d/0x9d0 kernel/bpf/stackmap.c:141
 __bpf_get_stack+0x4ad/0x5a0 kernel/bpf/stackmap.c:449
 ____bpf_get_stack_raw_tp kernel/trace/bpf_trace.c:1985 [inline]
 bpf_get_stack_raw_tp+0x1a3/0x240 kernel/trace/bpf_trace.c:1975
 bpf_prog_5c8cb7646b59f521+0x42/0x46
 bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
 __bpf_prog_run include/linux/filter.h:657 [inline]
 bpf_prog_run include/linux/filter.h:664 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
 bpf_trace_run2+0x204/0x420 kernel/trace/bpf_trace.c:2420
 trace_tlb_flush+0xfa/0x120 include/trace/events/tlb.h:38
 switch_mm_irqs_off+0x7cb/0xae0
 context_switch kernel/sched/core.c:5393 [inline]
 __schedule+0x1054/0x4a20 kernel/sched/core.c:6736
 __schedule_loop kernel/sched/core.c:6813 [inline]
 schedule+0x14b/0x320 kernel/sched/core.c:6828
 exit_to_user_mode_loop kernel/entry/common.c:96 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 irqentry_exit_to_user_mode+0xe7/0x270 kernel/entry/common.c:225
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0033:0x7fe38f639ba5
Code: Unable to access opcode bytes at 0x7fe38f639b7b.
RSP: 002b:00007ffe0d7da5f0 EFLAGS: 00000a87
RAX: 00000000984f6378 RBX: 00007fe38f7ac018 RCX: 0000000000000415
RDX: ffffffff81408dcc RSI: 0000000080000000 RDI: 00000000984f6378
RBP: 0000000081408000 R08: 0000001b31220000 R09: 0000000000000dcd
R10: 0000000081372dd1 R11: 0000000000000000 R12: 0000000000000415
R13: 0000000000000001 R14: 00007fe38f7a0000 R15: ffffffff81408dcc
 </TASK>


---
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If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [mm?] possible deadlock in __mmap_lock_do_trace_start_locking

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    36534d3c5453 tcp: use signed arithmetic in tcp_rtx_probe0_..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=110e9dde980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=333ebe38d43c42e2
dashboard link: https://syzkaller.appspot.com/bug?extid=6ff90931779bcdfc840c
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1585acfa980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17bdb7ee980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4e648f638b5f/disk-36534d3c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bbe0d41240f1/vmlinux-36534d3c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/17eb17ecd214/bzImage-36534d3c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6ff90931779bcdfc840c@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
6.10.0-rc2-syzkaller-00242-g36534d3c5453 #0 Not tainted
--------------------------------------------
syz-executor181/5090 is trying to acquire lock:
ffff8880b9538828 (lock#9){+.+.}-{2:2}, at: local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
ffff8880b9538828 (lock#9){+.+.}-{2:2}, at: __mmap_lock_do_trace_start_locking+0x83/0x620 mm/mmap_lock.c:230

but task is already holding lock:
ffff8880b9538828 (lock#9){+.+.}-{2:2}, at: local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
ffff8880b9538828 (lock#9){+.+.}-{2:2}, at: __mmap_lock_do_trace_start_locking+0x83/0x620 mm/mmap_lock.c:230

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(lock#9);
  lock(lock#9);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by syz-executor181/5090:
 #0: ffff8880b9538828 (lock#9){+.+.}-{2:2}, at: local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
 #0: ffff8880b9538828 (lock#9){+.+.}-{2:2}, at: __mmap_lock_do_trace_start_locking+0x83/0x620 mm/mmap_lock.c:230
 #1: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
 #1: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
 #1: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: get_mem_cgroup_from_mm+0x38/0x2a0 mm/memcontrol.c:1265
 #2: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: trace_call_bpf+0xbc/0x8a0

stack backtrace:
CPU: 1 PID: 5090 Comm: syz-executor181 Not tainted 6.10.0-rc2-syzkaller-00242-g36534d3c5453 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 check_deadlock kernel/locking/lockdep.c:3062 [inline]
 validate_chain+0x15d3/0x5900 kernel/locking/lockdep.c:3856
 __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
 local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
 __mmap_lock_do_trace_start_locking+0x9c/0x620 mm/mmap_lock.c:230
 __mmap_lock_trace_start_locking include/linux/mmap_lock.h:29 [inline]
 mmap_read_trylock include/linux/mmap_lock.h:162 [inline]
 stack_map_get_build_id_offset+0x98a/0x9d0 kernel/bpf/stackmap.c:141
 __bpf_get_stack+0x4ad/0x5a0 kernel/bpf/stackmap.c:449
 bpf_prog_e6cf5f9c69743609+0x42/0x46
 bpf_dispatcher_nop_func include/linux/bpf.h:1243 [inline]
 __bpf_prog_run include/linux/filter.h:691 [inline]
 bpf_prog_run include/linux/filter.h:698 [inline]
 bpf_prog_run_array include/linux/bpf.h:2103 [inline]
 trace_call_bpf+0x369/0x8a0 kernel/trace/bpf_trace.c:147
 perf_trace_run_bpf_submit+0x7c/0x1d0 kernel/events/core.c:10269
 perf_trace_lock+0x388/0x490 include/trace/events/lock.h:50
 trace_lock_release include/trace/events/lock.h:69 [inline]
 lock_release+0x986/0x9f0 kernel/locking/lockdep.c:5765
 rcu_lock_release include/linux/rcupdate.h:339 [inline]
 rcu_read_unlock include/linux/rcupdate.h:812 [inline]
 get_mem_cgroup_from_mm+0x1ad/0x2a0 mm/memcontrol.c:1271
 get_mm_memcg_path+0x1b/0x600 mm/mmap_lock.c:202
 __mmap_lock_do_trace_start_locking+0x134/0x620 mm/mmap_lock.c:230
 __mmap_lock_trace_start_locking include/linux/mmap_lock.h:29 [inline]
 mmap_read_lock include/linux/mmap_lock.h:143 [inline]
 acct_collect+0x7e7/0x830 kernel/acct.c:563
 do_exit+0x936/0x27e0 kernel/exit.c:853
 do_group_exit+0x207/0x2c0 kernel/exit.c:1023
 __do_sys_exit_group kernel/exit.c:1034 [inline]
 __se_sys_exit_group kernel/exit.c:1032 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1032
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9c47742279
Code: 90 49 c7 c0 b8 ff ff ff be e7 00 00 00 ba 3c 00 00 00 eb 12 0f 1f 44 00 00 89 d0 0f 05 48 3d 00 f0 ff ff 77 1c f4 89 f0 0f 05 <48> 3d 00 f0 ff ff 76 e7 f7 d8 64 41 89 00 eb df 0f 1f 80 00 00 00
RSP: 002b:00007ffd321ae558 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9c47742279
RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
RBP: 00007f9c477bd2b0 R08: ffffffffffffffb8 R09: 00000000000000a0
R10: 00000000000000a0 R11: 0000000000000246 R12: 00007f9c477bd2b0
R13: 0000000000000000 R14: 00007f9c477bdd20 R15: 00007f9c47713400
 </TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [mm?] possible deadlock in __mmap_lock_do_trace_start_locking

[syzbot]

syzbot has bisected this issue to:

commit 21c38a3bd4ee3fb7337d013a638302fb5e5f9dc2
Author: Jesper Dangaard Brouer <hawk@kernel.org>
Date:   Wed May 1 14:04:11 2024 +0000

    cgroup/rstat: add cgroup_rstat_cpu_lock helpers and tracepoints

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16695261980000
start commit:   36534d3c5453 tcp: use signed arithmetic in tcp_rtx_probe0_..
git tree:       bpf
final oops:     https://syzkaller.appspot.com/x/report.txt?x=15695261980000
console output: https://syzkaller.appspot.com/x/log.txt?x=11695261980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=333ebe38d43c42e2
dashboard link: https://syzkaller.appspot.com/bug?extid=6ff90931779bcdfc840c
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1585acfa980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17bdb7ee980000

Reported-by: syzbot+6ff90931779bcdfc840c@syzkaller.appspotmail.com
Fixes: 21c38a3bd4ee ("cgroup/rstat: add cgroup_rstat_cpu_lock helpers and tracepoints")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] [mm?] possible deadlock in __mmap_lock_do_trace_start_locking

[Waiman Long]

On 6/16/24 10:05, syzbot wrote:
> syzbot has bisected this issue to:
>
> commit 21c38a3bd4ee3fb7337d013a638302fb5e5f9dc2
> Author: Jesper Dangaard Brouer <hawk@kernel.org>
> Date:   Wed May 1 14:04:11 2024 +0000
>
>      cgroup/rstat: add cgroup_rstat_cpu_lock helpers and tracepoints
>
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16695261980000
> start commit:   36534d3c5453 tcp: use signed arithmetic in tcp_rtx_probe0_..
> git tree:       bpf
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=15695261980000
> console output: https://syzkaller.appspot.com/x/log.txt?x=11695261980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=333ebe38d43c42e2
> dashboard link: https://syzkaller.appspot.com/bug?extid=6ff90931779bcdfc840c
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1585acfa980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17bdb7ee980000
>
> Reported-by: syzbot+6ff90931779bcdfc840c@syzkaller.appspotmail.com
> Fixes: 21c38a3bd4ee ("cgroup/rstat: add cgroup_rstat_cpu_lock helpers and tracepoints")
>
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>
+static __always_inline
+unsigned long _cgroup_rstat_cpu_lock(raw_spinlock_t *cpu_lock, int cpu,
+                                    struct cgroup *cgrp, const bool 
fast_path)
+{
+       unsigned long flags;
+       bool contended;
+
+       /*
+        * The _irqsave() is needed because cgroup_rstat_lock is
+        * spinlock_t which is a sleeping lock on PREEMPT_RT. Acquiring
+        * this lock with the _irq() suffix only disables interrupts on
+        * a non-PREEMPT_RT kernel. The raw_spinlock_t below disables
+        * interrupts on both configurations. The _irqsave() ensures
+        * that interrupts are always disabled and later restored.
+        */
+       contended = !raw_spin_trylock_irqsave(cpu_lock, flags);
+       if (contended) {
+               if (fast_path)
+ trace_cgroup_rstat_cpu_lock_contended_fastpath(cgrp, cp>
+               else
+                       trace_cgroup_rstat_cpu_lock_contended(cgrp, cpu, 
conten>
+
+               raw_spin_lock_irqsave(cpu_lock, flags);
+       }

I believe the problem may be caused by the fact that 
trace_cgroup_rstat_cpu_lock_contended*() can be called with IRQ enabled. 
I had suggested before IRQ should be disabled first before doing any 
trace operation. See

https://lore.kernel.org/linux-mm/203fdb35-f4cf-4754-9709-3c024eecade9@redhat.com/

Doing so may be able to resolve this possible deadlock.

Cheers,
Longman

Re: [syzbot] [mm?] possible deadlock in __mmap_lock_do_trace_start_locking

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 7d6be67cfdd4a53cea7147313ca13c531e3a470f
Author: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date:   Fri Jun 21 01:08:41 2024 +0000

    mm: mmap_lock: replace get_memcg_path_buf() with on-stack buffer

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1412f697980000
start commit:   36534d3c5453 tcp: use signed arithmetic in tcp_rtx_probe0_..
git tree:       bpf
kernel config:  https://syzkaller.appspot.com/x/.config?x=333ebe38d43c42e2
dashboard link: https://syzkaller.appspot.com/bug?extid=6ff90931779bcdfc840c
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1585acfa980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17bdb7ee980000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: mm: mmap_lock: replace get_memcg_path_buf() with on-stack buffer

For information about bisection process see: https://goo.gl/tpsmEJ#bisection