[syzbot] [perf?] WARNING: suspicious RCU usage in get_callchain_entry

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c942a0cd3603 Merge tag 'for_linus' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12ef0aef180000
kernel config: https://syzkaller.appspot.com/x/.config?x=545d4b3e07d6ccbc
dashboard link: https://syzkaller.appspot.com/bug?extid=72a43cdb78469f7fbad1
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11c4d490980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=138bf96b180000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-c942a0cd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/02773b27b0d3/vmlinux-c942a0cd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/669bed7ebf5d/bzImage-c942a0cd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+72a43c...@syzkaller.appspotmail.com

=============================
WARNING: suspicious RCU usage
6.9.0-rc5-syzkaller-00159-gc942a0cd3603 #0 Not tainted
-----------------------------
kernel/events/callchain.c:161 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz-executor305/5180:
#0: ffffffff8d7b04c0 (rcu_read_lock_trace){....}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
#0: ffffffff8d7b04c0 (rcu_read_lock_trace){....}-{0:0}, at: rcu_read_lock_trace include/linux/rcupdate_trace.h:57 [inline]
#0: ffffffff8d7b04c0 (rcu_read_lock_trace){....}-{0:0}, at: bpf_prog_test_run_syscall+0x345/0x770 net/bpf/test_run.c:1508

stack backtrace:
CPU: 3 PID: 5180 Comm: syz-executor305 Not tainted 6.9.0-rc5-syzkaller-00159-gc942a0cd3603 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:114
lockdep_rcu_suspicious+0x20b/0x3b0 kernel/locking/lockdep.c:6712
get_callchain_entry+0x274/0x3f0 kernel/events/callchain.c:161
get_perf_callchain+0xdc/0x5a0 kernel/events/callchain.c:187
__bpf_get_stack+0x4d9/0x700 kernel/bpf/stackmap.c:435
____bpf_get_stack_raw_tp kernel/trace/bpf_trace.c:1985 [inline]
bpf_get_stack_raw_tp+0x124/0x160 kernel/trace/bpf_trace.c:1975
___bpf_prog_run+0x3e51/0xabd0 kernel/bpf/core.c:1997
__bpf_prog_run32+0xc1/0x100 kernel/bpf/core.c:2236
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_prog_run_pin_on_cpu include/linux/filter.h:681 [inline]
bpf_prog_test_run_syscall+0x3ae/0x770 net/bpf/test_run.c:1509
bpf_prog_test_run kernel/bpf/syscall.c:4269 [inline]
__sys_bpf+0xd56/0x4b40 kernel/bpf/syscall.c:5678
__do_sys_bpf kernel/bpf/syscall.c:5767 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5765 [inline]
__x64_sys_bpf+0x78/0xc0 kernel/bpf/syscall.c:5765
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcf/0x260 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f54610dc669
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff4b9fae08 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007fff4b9fafd8 RCX: 00007f54610dc669
RDX: 000000000000000c RSI: 00000000200004c0 RDI: 000000000000000a
RBP: 00007f546114f610 R08: 00007fff4b9fafd8 R09: 00007fff4b9fafd8
R10: 00007fff4b9fafd8 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fff4b9fafc8 R14: 0000000000000001 R15: 0000000000000001
</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 syzk...@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 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.

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

[Qing Wang]

#syz test

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index da3d328f5c15..6e53c2d916cd 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -460,8 +460,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,

max_depth = stack_map_calculate_max_depth(size, elem_size, flags);

- if (may_fault)
- rcu_read_lock(); /* need RCU for perf's callchain below */
+ rcu_read_lock(); /* need RCU for perf's callchain below */

if (trace_in) {
trace = trace_in;
@@ -474,8 +473,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
}

if (unlikely(!trace) || trace->nr < skip) {
- if (may_fault)
- rcu_read_unlock();
+ rcu_read_unlock();
goto err_fault;
}

[Qing Wang]

#syz test

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c

index da3d328f5c15..f97d4aa9d038 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -460,7 +460,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,

max_depth = stack_map_calculate_max_depth(size, elem_size, flags);

- if (may_fault)

+ if (!trace_in)

rcu_read_lock(); /* need RCU for perf's callchain below */

if (trace_in) {

@@ -474,7 +474,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,

}

if (unlikely(!trace) || trace->nr < skip) {
- if (may_fault)

+ if (!trace_in)
rcu_read_unlock();
goto err_fault;
}
@@ -494,7 +494,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
}

/* trace/ips should not be dereferenced after this point */
- if (may_fault)
+ if (!trace_in)
rcu_read_unlock();

if (user_build_id)

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: sleeping function called from invalid context in bpf_prog_test_run_syscall

BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:201
in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 6641, name: syz.0.17
preempt_count: 0, expected: 0
RCU nest depth: 1, expected: 0
1 lock held by syz.0.17/6641:
#0: ffffffff8dbc77c0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
#0: ffffffff8dbc77c0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
#0: ffffffff8dbc77c0 (rcu_read_lock){....}-{1:3}, at: __bpf_get_stack+0x269/0xab0 kernel/bpf/stackmap.c:463
CPU: 1 UID: 0 PID: 6641 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
__might_resched+0x329/0x480 kernel/sched/core.c:8829
__might_fault+0x76/0x130 mm/memory.c:7175
_inline_copy_to_user include/linux/uaccess.h:201 [inline]
_copy_to_user+0x2c/0xb0 lib/usercopy.c:26
copy_to_user include/linux/uaccess.h:236 [inline]
bpf_prog_test_run_syscall+0x337/0x4c0 net/bpf/test_run.c:1642
bpf_prog_test_run+0x2cd/0x340 kernel/bpf/syscall.c:4703
__sys_bpf+0x5cb/0x920 kernel/bpf/syscall.c:6182
__do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6272
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efdae6faeb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007efdadd5e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007efdae975fa0 RCX: 00007efdae6faeb9
RDX: 000000000000000c RSI: 00002000000004c0 RDI: 000000000000000a
RBP: 00007efdae768c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efdae976038 R14: 00007efdae975fa0 R15: 00007fffcdbbfb78
</TASK>

=============================
[ BUG: Invalid wait context ]
syzkaller #0 Tainted: G W
-----------------------------
syz.0.17/6641 is trying to lock:
ffff88803daa5cf0 (&mm->mmap_lock){++++}-{4:4}, at: __might_fault+0xaf/0x130 mm/memory.c:7177

other info that might help us debug this:

context-{5:5}
1 lock held by syz.0.17/6641:
#0: ffffffff8dbc77c0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
#0: ffffffff8dbc77c0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
#0: ffffffff8dbc77c0 (rcu_read_lock){....}-{1:3}, at: __bpf_get_stack+0x269/0xab0 kernel/bpf/stackmap.c:463
stack backtrace:
CPU: 1 UID: 0 PID: 6641 Comm: syz.0.17 Tainted: G W syzkaller #0 PREEMPT_{RT,(full)}
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_lock_invalid_wait_context kernel/locking/lockdep.c:4830 [inline]
check_wait_context kernel/locking/lockdep.c:4902 [inline]
__lock_acquire+0xec1/0x2cf0 kernel/locking/lockdep.c:5187
lock_acquire+0x106/0x330 kernel/locking/lockdep.c:5868
__might_fault+0xcb/0x130 mm/memory.c:7177
_inline_copy_to_user include/linux/uaccess.h:201 [inline]
_copy_to_user+0x2c/0xb0 lib/usercopy.c:26
copy_to_user include/linux/uaccess.h:236 [inline]
bpf_prog_test_run_syscall+0x337/0x4c0 net/bpf/test_run.c:1642
bpf_prog_test_run+0x2cd/0x340 kernel/bpf/syscall.c:4703
__sys_bpf+0x5cb/0x920 kernel/bpf/syscall.c:6182
__do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:6272
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efdae6faeb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007efdadd5e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007efdae975fa0 RCX: 00007efdae6faeb9
RDX: 000000000000000c RSI: 00002000000004c0 RDI: 000000000000000a
RBP: 00007efdae768c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efdae976038 R14: 00007efdae975fa0 R15: 00007fffcdbbfb78
</TASK>


Tested on:

commit: 1f97d9dc Merge tag 'vfio-v6.19-rc8' of https://github...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1573a6ef980000
kernel config: https://syzkaller.appspot.com/x/.config?x=151a39927f1e10b4
dashboard link: https://syzkaller.appspot.com/bug?extid=72a43cdb78469f7fbad1
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
patch: https://syzkaller.appspot.com/x/patch.diff?x=14eb785a580000

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+72a43c...@syzkaller.appspotmail.com
Tested-by: syzbot+72a43c...@syzkaller.appspotmail.com

Tested on:

commit: 1f97d9dc Merge tag 'vfio-v6.19-rc8' of https://github...
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=170ba6ef980000

kernel config: https://syzkaller.appspot.com/x/.config?x=151a39927f1e10b4
dashboard link: https://syzkaller.appspot.com/bug?extid=72a43cdb78469f7fbad1
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=13b7718a580000

Note: testing is done by a robot and is best-effort only.

[Peter Zijlstra]

This is just papering over more bugs. There was a series out there
somewhere trying to fix up this code, let me see if I can find it in
this shitshow called an inbox :/

[Qing Wang]

On Wed, 28 Jan 2026 at 16:52, Peter Zijlstra <pet...@infradead.org> wrote:
> This is just papering over more bugs. There was a series out there
> somewhere trying to fix up this code, let me see if I can find it in
> this shitshow called an inbox :/

Thank you for reminding me. I found that fix you said.

https://lore.kernel.org/bpf/fb745675-e25c-4dcc...@linux.dev/T/#mf901967ebe77506f1bd6e3d876c2a85824d9519d

Let's ignore this patch :)

--
Best regards,
Qing

[Qing Wang]

#syz test

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 75495a5c3507..ee3d8ed11699 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -84,6 +84,7 @@ static struct bpf_raw_event_map *bpf_get_raw_tracepoint_module(const char *name)

u64 bpf_get_stackid(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
u64 bpf_get_stack(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
+u64 bpf_get_stack_sleepable(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);

static int bpf_btf_printf_prepare(struct btf_ptr *ptr, u32 btf_ptr_size,
u64 flags, const struct btf **btf,
@@ -1705,6 +1706,32 @@ static const struct bpf_func_proto bpf_get_stack_proto_raw_tp = {
.arg4_type = ARG_ANYTHING,
};

+BPF_CALL_4(bpf_get_stack_sleepable_raw_tp, struct bpf_raw_tracepoint_args *, args,
+ void *, buf, u32, size, u64, flags)
+{
+ struct pt_regs *regs = get_bpf_raw_tp_regs();
+ int ret;
+
+ if (IS_ERR(regs))
+ return PTR_ERR(regs);
+
+ perf_fetch_caller_regs(regs);
+ ret = bpf_get_stack_sleepable((unsigned long) regs, (unsigned long) buf,
+ (unsigned long) size, flags, 0);
+ put_bpf_raw_tp_regs();
+ return ret;
+}
+
+static const struct bpf_func_proto bpf_get_stack_sleepable_proto_raw_tp = {
+ .func = bpf_get_stack_sleepable_raw_tp,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_CTX,
+ .arg2_type = ARG_PTR_TO_UNINIT_MEM,
+ .arg3_type = ARG_CONST_SIZE_OR_ZERO,
+ .arg4_type = ARG_ANYTHING,
+};
+
static const struct bpf_func_proto *
raw_tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
{
@@ -1714,7 +1741,8 @@ raw_tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
case BPF_FUNC_get_stackid:
return &bpf_get_stackid_proto_raw_tp;
case BPF_FUNC_get_stack:
- return &bpf_get_stack_proto_raw_tp;
+ return prog->sleepable ? &bpf_get_stack_sleepable_proto_raw_tp
+ : &bpf_get_stack_proto_raw_tp;
case BPF_FUNC_get_attach_cookie:
return &bpf_get_attach_cookie_proto_tracing;
default:

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+72a43c...@syzkaller.appspotmail.com
Tested-by: syzbot+72a43c...@syzkaller.appspotmail.com

Tested on:

commit: f5bbbfec Merge tag 'probes-fixes-v7.2-rc7' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17a47132580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d07fbc6821d72a61
dashboard link: https://syzkaller.appspot.com/bug?extid=72a43cdb78469f7fbad1
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch: https://syzkaller.appspot.com/x/patch.diff?x=1604b479580000