[syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    2c22dc1ee3a1 Merge tag 'mailbox-v6.13' of git://git.kernel..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17f2bee8580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8df9bf3383f5970
dashboard link: https://syzkaller.appspot.com/bug?extid=97da3d7e0112d59971de
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/9137c3e19e21/disk-2c22dc1e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1aad80837d89/vmlinux-2c22dc1e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d7979d71d6d2/bzImage-2c22dc1e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+97da3d7e0112d59971de@syzkaller.appspotmail.com

=============================
[ BUG: Invalid wait context ]
6.12.0-syzkaller-09435-g2c22dc1ee3a1 #0 Not tainted
-----------------------------
iou-wrk-9958/9967 is trying to lock:
ffff88802744ae58 (&sighand->siglock){-.-.}-{3:3}, at: __lock_task_sighand+0x149/0x2d0 kernel/signal.c:1379
other info that might help us debug this:
context-{5:5}
3 locks held by iou-wrk-9958/9967:
 #0: ffff88814d2870c0 (&acct->lock){+.+.}-{2:2}, at: io_acct_run_queue io_uring/io-wq.c:260 [inline]
 #0: ffff88814d2870c0 (&acct->lock){+.+.}-{2:2}, at: io_wq_worker+0x44b/0xed0 io_uring/io-wq.c:654
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2350 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: bpf_trace_run2+0x1fc/0x540 kernel/trace/bpf_trace.c:2392
 #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: __lock_task_sighand+0x29/0x2d0 kernel/signal.c:1362
stack backtrace:
CPU: 1 UID: 0 PID: 9967 Comm: iou-wrk-9958 Not tainted 6.12.0-syzkaller-09435-g2c22dc1ee3a1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_lock_invalid_wait_context kernel/locking/lockdep.c:4826 [inline]
 check_wait_context kernel/locking/lockdep.c:4898 [inline]
 __lock_acquire+0x15a8/0x2100 kernel/locking/lockdep.c:5176
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
 __lock_task_sighand+0x149/0x2d0 kernel/signal.c:1379
 lock_task_sighand include/linux/sched/signal.h:743 [inline]
 do_send_sig_info kernel/signal.c:1267 [inline]
 group_send_sig_info+0x274/0x310 kernel/signal.c:1418
 bpf_send_signal_common+0x3c4/0x630 kernel/trace/bpf_trace.c:881
 ____bpf_send_signal kernel/trace/bpf_trace.c:886 [inline]
 bpf_send_signal+0x1d/0x30 kernel/trace/bpf_trace.c:884
 bpf_prog_631417f49dd64198+0x25/0x48
 bpf_dispatcher_nop_func include/linux/bpf.h:1290 [inline]
 __bpf_prog_run include/linux/filter.h:701 [inline]
 bpf_prog_run include/linux/filter.h:708 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2351 [inline]
 bpf_trace_run2+0x2ec/0x540 kernel/trace/bpf_trace.c:2392
 trace_contention_end+0x114/0x140 include/trace/events/lock.h:122
 __pv_queued_spin_lock_slowpath+0xb7e/0xdb0 kernel/locking/qspinlock.c:557
 pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:584 [inline]
 queued_spin_lock_slowpath+0x42/0x50 arch/x86/include/asm/qspinlock.h:51
 queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
 do_raw_spin_lock+0x272/0x370 kernel/locking/spinlock_debug.c:116
 io_acct_run_queue io_uring/io-wq.c:260 [inline]
 io_wq_worker+0x44b/0xed0 io_uring/io-wq.c:654
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>


---
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Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[Alexei Starovoitov]

Puranjay, Andrii and All,

looks like if (irqs_disabled()) is not enough.
Should we change it to preemptible() ?

It will likely make it async all the time,
but in this it's an ok trade off?


On Thu, Nov 28, 2024 at 5:07 AM syzbot
<syzbot+97da3d7e0112d59971de@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    2c22dc1ee3a1 Merge tag 'mailbox-v6.13' of git://git.kernel..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17f2bee8580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8df9bf3383f5970
> dashboard link: https://syzkaller.appspot.com/bug?extid=97da3d7e0112d59971de
> 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/9137c3e19e21/disk-2c22dc1e.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/1aad80837d89/vmlinux-2c22dc1e.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/d7979d71d6d2/bzImage-2c22dc1e.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+97da3d7e0112d59971de@syzkaller.appspotmail.com
>
> =============================
> [ BUG: Invalid wait context ]
> 6.12.0-syzkaller-09435-g2c22dc1ee3a1 #0 Not tainted
> -----------------------------
> iou-wrk-9958/9967 is trying to lock:
> ffff88802744ae58 (&sighand->siglock){-.-.}-{3:3}, at: __lock_task_sighand+0x149/0x2d0 kernel/signal.c:1379
> other info that might help us debug this:
> context-{5:5}
> 3 locks held by iou-wrk-9958/9967:
>  #0: ffff88814d2870c0 (&acct->lock){+.+.}-{2:2}, at: io_acct_run_queue io_uring/io-wq.c:260 [inline]
>  #0: ffff88814d2870c0 (&acct->lock){+.+.}-{2:2}, at: io_wq_worker+0x44b/0xed0 io_uring/io-wq.c:654
>  #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
>  #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
>  #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2350 [inline]
>  #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: bpf_trace_run2+0x1fc/0x540 kernel/trace/bpf_trace.c:2392
>  #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
>  #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
>  #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: __lock_task_sighand+0x29/0x2d0 kernel/signal.c:1362
> stack backtrace:
> CPU: 1 UID: 0 PID: 9967 Comm: iou-wrk-9958 Not tainted 6.12.0-syzkaller-09435-g2c22dc1ee3a1 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>  print_lock_invalid_wait_context kernel/locking/lockdep.c:4826 [inline]
>  check_wait_context kernel/locking/lockdep.c:4898 [inline]
>  __lock_acquire+0x15a8/0x2100 kernel/locking/lockdep.c:5176
>  lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>  _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
>  __lock_task_sighand+0x149/0x2d0 kernel/signal.c:1379
>  lock_task_sighand include/linux/sched/signal.h:743 [inline]
>  do_send_sig_info kernel/signal.c:1267 [inline]
>  group_send_sig_info+0x274/0x310 kernel/signal.c:1418
>  bpf_send_signal_common+0x3c4/0x630 kernel/trace/bpf_trace.c:881
>  ____bpf_send_signal kernel/trace/bpf_trace.c:886 [inline]
>  bpf_send_signal+0x1d/0x30 kernel/trace/bpf_trace.c:884
>  bpf_prog_631417f49dd64198+0x25/0x48
>  bpf_dispatcher_nop_func include/linux/bpf.h:1290 [inline]
>  __bpf_prog_run include/linux/filter.h:701 [inline]
>  bpf_prog_run include/linux/filter.h:708 [inline]
>  __bpf_trace_run kernel/trace/bpf_trace.c:2351 [inline]
>  bpf_trace_run2+0x2ec/0x540 kernel/trace/bpf_trace.c:2392
>  trace_contention_end+0x114/0x140 include/trace/events/lock.h:122
>  __pv_queued_spin_lock_slowpath+0xb7e/0xdb0 kernel/locking/qspinlock.c:557
>  pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:584 [inline]
>  queued_spin_lock_slowpath+0x42/0x50 arch/x86/include/asm/qspinlock.h:51
>  queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
>  do_raw_spin_lock+0x272/0x370 kernel/locking/spinlock_debug.c:116
>  io_acct_run_queue io_uring/io-wq.c:260 [inline]
>  io_wq_worker+0x44b/0xed0 io_uring/io-wq.c:654
>  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>  </TASK>
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    45e04eb4d9d8 bpf: Refactor bpf_tracing_func_proto() and re..
git tree:       bpf-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=167e17c0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fb680913ee293bcc
dashboard link: https://syzkaller.appspot.com/bug?extid=97da3d7e0112d59971de
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=114a7d30580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1395ff78580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f45e1a59de79/disk-45e04eb4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6e2405d2c818/vmlinux-45e04eb4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2c2415798034/bzImage-45e04eb4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+97da3d7e0112d59971de@syzkaller.appspotmail.com

=============================
[ BUG: Invalid wait context ]
6.12.0-syzkaller-g45e04eb4d9d8 #0 Not tainted
-----------------------------
syz-executor227/5855 is trying to lock:
ffff8880262a8018 (&sighand->siglock){-...}-{3:3}, at: __lock_task_sighand+0x149/0x2d0 kernel/signal.c:1379
other info that might help us debug this:
context-{5:5}
8 locks held by syz-executor227/5855:
 #0: ffff88802f97ea90 (&vma->vm_lock->lock){++++}-{4:4}, at: vma_start_read include/linux/mm.h:716 [inline]
 #0: ffff88802f97ea90 (&vma->vm_lock->lock){++++}-{4:4}, at: lock_vma_under_rcu+0x34b/0x790 mm/memory.c:6278
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: do_fault_around mm/memory.c:5279 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: do_read_fault mm/memory.c:5313 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: do_fault mm/memory.c:5456 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: do_pte_missing mm/memory.c:3979 [inline]
 #1: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: handle_pte_fault+0x21c3/0x68a0 mm/memory.c:5801
 #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #2: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: filemap_map_pages+0x243/0x20d0 mm/filemap.c:3645
 #3: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #3: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #3: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: __pte_offset_map+0x82/0x380 mm/pgtable-generic.c:287
 #4: ffff8880791b2df8 (ptlock_ptr(ptdesc)#2){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #4: ffff8880791b2df8 (ptlock_ptr(ptdesc)#2){+.+.}-{3:3}, at: __pte_offset_map_lock+0x1ba/0x300 mm/pgtable-generic.c:402
 #5: ffffffff8e93c4a0 (rcu_read_lock_sched){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #5: ffffffff8e93c4a0 (rcu_read_lock_sched){....}-{1:2}, at: rcu_read_lock_sched include/linux/rcupdate.h:941 [inline]
 #5: ffffffff8e93c4a0 (rcu_read_lock_sched){....}-{1:2}, at: pfn_valid+0xf6/0x450 include/linux/mmzone.h:2048
 #6: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: trace_call_bpf+0xbc/0x8a0
 #7: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #7: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #7: ffffffff8e93c520 (rcu_read_lock){....}-{1:3}, at: __lock_task_sighand+0x29/0x2d0 kernel/signal.c:1362
stack backtrace:
CPU: 0 UID: 0 PID: 5855 Comm: syz-executor227 Not tainted 6.12.0-syzkaller-g45e04eb4d9d8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_lock_invalid_wait_context kernel/locking/lockdep.c:4826 [inline]
 check_wait_context kernel/locking/lockdep.c:4898 [inline]
 __lock_acquire+0x15a8/0x2100 kernel/locking/lockdep.c:5176
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
 __lock_task_sighand+0x149/0x2d0 kernel/signal.c:1379
 lock_task_sighand include/linux/sched/signal.h:743 [inline]
 do_send_sig_info kernel/signal.c:1267 [inline]
 group_send_sig_info+0x274/0x310 kernel/signal.c:1418
 bpf_send_signal_common+0x3c4/0x630 kernel/trace/bpf_trace.c:870
 ____bpf_send_signal_thread kernel/trace/bpf_trace.c:887 [inline]
 bpf_send_signal_thread+0x1a/0x30 kernel/trace/bpf_trace.c:885
 bpf_prog_b7be628660dc1b90+0x23/0x29
 bpf_dispatcher_nop_func include/linux/bpf.h:1290 [inline]
 __bpf_prog_run include/linux/filter.h:701 [inline]
 bpf_prog_run include/linux/filter.h:708 [inline]
 bpf_prog_run_array include/linux/bpf.h:2177 [inline]
 trace_call_bpf+0x369/0x8a0 kernel/trace/bpf_trace.c:146
 perf_trace_run_bpf_submit+0x82/0x180 kernel/events/core.c:10473
 do_perf_trace_lock include/trace/events/lock.h:50 [inline]
 perf_trace_lock+0x388/0x490 include/trace/events/lock.h:50
 trace_lock_release include/trace/events/lock.h:69 [inline]
 lock_release+0x9cc/0xa30 kernel/locking/lockdep.c:5860
 rcu_lock_release include/linux/rcupdate.h:347 [inline]
 rcu_read_unlock_sched include/linux/rcupdate.h:962 [inline]
 pfn_valid+0x3eb/0x450 include/linux/mmzone.h:2058
 page_table_check_set+0x22/0x540 mm/page_table_check.c:110
 __page_table_check_ptes_set+0x30f/0x410 mm/page_table_check.c:225
 page_table_check_ptes_set include/linux/page_table_check.h:74 [inline]
 set_ptes include/linux/pgtable.h:288 [inline]
 set_pte_range+0x724/0x750 mm/memory.c:5067
 filemap_map_order0_folio mm/filemap.c:3624 [inline]
 filemap_map_pages+0x11c6/0x20d0 mm/filemap.c:3678
 do_fault_around mm/memory.c:5280 [inline]
 do_read_fault mm/memory.c:5313 [inline]
 do_fault mm/memory.c:5456 [inline]
 do_pte_missing mm/memory.c:3979 [inline]
 handle_pte_fault+0x31d6/0x68a0 mm/memory.c:5801
 __handle_mm_fault mm/memory.c:5944 [inline]
 handle_mm_fault+0x1106/0x1bb0 mm/memory.c:6112
 do_user_addr_fault arch/x86/mm/fault.c:1338 [inline]
 handle_page_fault arch/x86/mm/fault.c:1481 [inline]
 exc_page_fault+0x459/0x8c0 arch/x86/mm/fault.c:1539
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
RIP: 0033:0x7f2c735865f8
Code: Unable to access opcode bytes at 0x7f2c735865ce.
RSP: 002b:00007ffcc6892fb8 EFLAGS: 00010202
RAX: 00007f2c735b6ad8 RBX: 0000000000000000 RCX: 0000000000000004
RDX: 00007f2c735b7ce0 RSI: 0000000000000000 RDI: 00007f2c735b6ad8
RBP: 00007f2c735b5118 R08: 00007f2c7350e2b0 R09: 00007f2c7350e2b0
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f2c735b7cc8
R13: 0000000000000000 R14: 00007f2c735b7ce0 R15: 00007f2c7350e590
 </TASK>


---
If you want syzbot to run the reproducer, reply with:
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Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[Puranjay Mohan]

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Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:

> Puranjay, Andrii and All,
>
> looks like if (irqs_disabled()) is not enough.
> Should we change it to preemptible() ?
>
> It will likely make it async all the time,
> but in this it's an ok trade off?
>

Yes, as BPF programs can run in all kinds of contexts.

We should replace 'if (irqs_disabled())' with 'if (!preemptible())'

because the definition is:

#define preemptible()	(preempt_count() == 0 && !irqs_disabled())

and we need if ((preempt_count() != 0) || irqs_disabled()), in both
these cases we want to make it async.

I will try to test the fix as Syzbot has now found a reproducer.

Thanks,
Puranjay

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Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[Alexei Starovoitov]

On Mon, Dec 2, 2024 at 4:42 AM Puranjay Mohan <puranjay@kernel.org> wrote:
>
> Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:
>
> > Puranjay, Andrii and All,
> >
> > looks like if (irqs_disabled()) is not enough.
> > Should we change it to preemptible() ?
> >
> > It will likely make it async all the time,
> > but in this it's an ok trade off?
> >
>
> Yes, as BPF programs can run in all kinds of contexts.
>
> We should replace 'if (irqs_disabled())' with 'if (!preemptible())'
>
> because the definition is:
>
> #define preemptible()   (preempt_count() == 0 && !irqs_disabled())
>
> and we need if ((preempt_count() != 0) || irqs_disabled()), in both
> these cases we want to make it async.
>
> I will try to test the fix as Syzbot has now found a reproducer.

Puranjay,

Any progress on a patch ?

Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[Alexei Starovoitov]

On Tue, Dec 17, 2024 at 3:49 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Dec 2, 2024 at 4:42 AM Puranjay Mohan <puranjay@kernel.org> wrote:
> >
> > Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:
> >
> > > Puranjay, Andrii and All,
> > >
> > > looks like if (irqs_disabled()) is not enough.
> > > Should we change it to preemptible() ?
> > >
> > > It will likely make it async all the time,
> > > but in this it's an ok trade off?
> > >
> >
> > Yes, as BPF programs can run in all kinds of contexts.
> >
> > We should replace 'if (irqs_disabled())' with 'if (!preemptible())'
> >
> > because the definition is:
> >
> > #define preemptible()   (preempt_count() == 0 && !irqs_disabled())
> >
> > and we need if ((preempt_count() != 0) || irqs_disabled()), in both
> > these cases we want to make it async.
> >
> > I will try to test the fix as Syzbot has now found a reproducer.
>
> Puranjay,
>
> Any progress on a patch ?

ping.

Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[Puranjay Mohan]

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Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:

> On Tue, Dec 17, 2024 at 3:49 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
>>
>> On Mon, Dec 2, 2024 at 4:42 AM Puranjay Mohan <puranjay@kernel.org> wrote:
>> >
>> > Alexei Starovoitov <alexei.starovoitov@gmail.com> writes:
>> >
>> > > Puranjay, Andrii and All,
>> > >
>> > > looks like if (irqs_disabled()) is not enough.
>> > > Should we change it to preemptible() ?
>> > >
>> > > It will likely make it async all the time,
>> > > but in this it's an ok trade off?
>> > >
>> >
>> > Yes, as BPF programs can run in all kinds of contexts.
>> >
>> > We should replace 'if (irqs_disabled())' with 'if (!preemptible())'
>> >
>> > because the definition is:
>> >
>> > #define preemptible()   (preempt_count() == 0 && !irqs_disabled())
>> >
>> > and we need if ((preempt_count() != 0) || irqs_disabled()), in both
>> > these cases we want to make it async.
>> >
>> > I will try to test the fix as Syzbot has now found a reproducer.
>>
>> Puranjay,
>>
>> Any progress on a patch ?
>
> ping.

Hi Alexei,
Sorry for being AWOL. I was on a long vacation in India and just got
back.

Here is the patch to fix this: https://lore.kernel.org/all/20250115103647.38487-1-puranjay@kernel.org/

Thanks,
Puranjay

#syz test: https://github.com/puranjaymohan/bpf.git bpf_preemt_fix

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Re: [syzbot] [bpf?] [trace?] WARNING: locking bug in __lock_task_sighand

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
lost connection to test machine



Tested on:

commit:         c547a7b6 bpf: trace: send signals asynchronously if !p..
git tree:       https://github.com/puranjaymohan/bpf.git bpf_preemt_fix
console output: https://syzkaller.appspot.com/x/log.txt?x=178257c4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=aadf89e2f6db86cc
dashboard link: https://syzkaller.appspot.com/bug?extid=97da3d7e0112d59971de
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.