Message-ID: <696d56b4.050a0220.3390f1.0027.GAE@google.com>
Date: Sun, 18 Jan 2026 13:55:00 -0800
From: syzbot <syzbot+8bb3e2bee8a429cc76dd@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Forwarded: Private message regarding: [syzbot] [mm?] INFO: rcu
 detected stall in sys_execve (6)

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***

Subject: Private message regarding: [syzbot] [mm?] INFO: rcu detected stall in sys_execve (6)
Author: kapoorarnav43@...il.com

#syz test

>From 4e8268fd6319d5b97ba6334b7f66fd0b1719b863 Mon Sep 17 00:00:00 2001
From: Arnav Kapoor <kapoorarnav43@...il.com>
Date: Mon, 19 Jan 2026 03:15:46 +0530
Subject: [PATCH] fs/exec: add cond_resched() in setup_arg_pages to prevent 
RCU
 stalls

Syzbot reported an RCU stall in sys_execve. The issue occurs when
setup_arg_pages() calls expand_stack_locked() which can perform memory
allocations that take significant time without yielding to the scheduler.
This prevents RCU grace periods from completing, leading to RCU stalls.

The fix is minimal: add cond_resched() after expand_stack_locked() returns,
allowing the scheduler to preempt if needed and permitting RCU grace periods
to complete.

Reported-by: syzbot+af59ca6e6cfb5db2946e165031b25d7f52ee60e9
Closes: 
https://syzkaller.appspot.com/bug?id=af59ca6e6cfb5db2946e165031b25d7f52ee60e9
Signed-off-by: Arnav Kapoor <kapoorarnav43@...il.com>
---
 fs/exec.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index 9d5ebc9d1..fb7ae929d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -712,6 +712,8 @@ int setup_arg_pages(struct linux_binprm *bprm,
 #endif
        current->mm->start_stack = bprm->p;
        ret = expand_stack_locked(vma, stack_base);
+        /* Allow RCU and scheduler to make progress. */
+        cond_resched();
        if (ret)
                ret = -EFAULT;
 
-- 
2.43.0

On Sunday, 18 January 2026 at 04:48:24 UTC+5:30 syzbot wrote:

syzbot has found a reproducer for the following issue on: 

HEAD commit: a74c7a58ca2c net: freescale: ucc_geth: Return early when T.. 
git tree: net 
console output: https://syzkaller.appspot.com/x/log.txt?x=16fdf39a580000 
kernel config: https://syzkaller.appspot.com/x/.config?x=323fe5bdde2384a5 
dashboard link: https://syzkaller.appspot.com/bug?extid=8bb3e2bee8a429cc76dd 
compiler: Debian clang version 20.1.8 
(++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 
20.1.8 
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13d8639a580000 
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=154863fa580000 

Downloadable assets: 
disk image: 
https://storage.googleapis.com/syzbot-assets/50a3e60a3908/disk-a74c7a58.raw.xz 
vmlinux: 
https://storage.googleapis.com/syzbot-assets/ee6a6a2a52e4/vmlinux-a74c7a58.xz 
kernel image: 
https://storage.googleapis.com/syzbot-assets/033a07d12b3e/bzImage-a74c7a58.xz 

The issue was bisected to: 

commit 5a781ccbd19e4664babcbe4b4ead7aa2b9283d22 
Author: Vinicius Costa Gomes <viniciu...@...el.com> 
Date: Sat Sep 29 00:59:43 2018 +0000 

tc: Add support for configuring the taprio scheduler 

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10311900580000 
final oops: https://syzkaller.appspot.com/x/report.txt?x=12311900580000 
console output: https://syzkaller.appspot.com/x/log.txt?x=14311900580000 

IMPORTANT: if you fix the issue, please add the following tag to the 
commit: 
Reported-by: syzbot+8bb3e2...@...kaller.appspotmail.com 
Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio 
scheduler") 

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: 
rcu: 1-...!: (1 GPs behind) idle=b674/1/0x4000000000000000 
softirq=16193/16205 fqs=2 
rcu: (detected by 0, t=10502 jiffies, g=13757, q=3905 ncpus=2) 
Sending NMI from CPU 0 to CPUs 1: 
NMI backtrace for cpu 1 
CPU: 1 UID: 0 PID: 6128 Comm: syz-executor Not tainted syzkaller #0 
PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS 
Google 10/25/2025 
RIP: 0010:rcu_is_watching_curr_cpu include/linux/context_tracking.h:128 
[inline] 
RIP: 0010:rcu_is_watching+0x3a/0xb0 kernel/rcu/tree.c:751 
Code: e8 bb 0d b3 09 89 c3 83 f8 08 73 65 49 bf 00 00 00 00 00 fc ff df 4c 
8d 34 dd d0 0d 9b 8d 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 <74> 08 4c 89 f7 
e8 8c 1d 80 00 48 c7 c3 d8 56 81 92 49 03 1e 48 89 
RSP: 0018:ffffc90000a08c70 EFLAGS: 00000046 
RAX: 1ffffffff1b361bb RBX: 0000000000000001 RCX: 0000000000010002 
RDX: 0000000000000000 RSI: ffffffff8bc086c0 RDI: ffffffff8bc08680 
RBP: ffffffff81ae6da2 R08: 0000000000000001 R09: 0000000000000000 
R10: dffffc0000000000 R11: fffffbfff1f045cf R12: 0000000000000000 
R13: ffff8880b8728258 R14: ffffffff8d9b0dd8 R15: dffffc0000000000 
FS: 0000000000000000(0000) GS:ffff888125f1e000(0000) knlGS:0000000000000000 
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 
CR2: 00007f9426807ff8 CR3: 0000000077a18000 CR4: 00000000003526f0 
Call Trace: 
<IRQ> 
trace_lock_acquire include/trace/events/lock.h:24 [inline] 
lock_acquire+0x5f/0x340 kernel/locking/lockdep.c:5831 
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline] 
_raw_spin_lock_irq+0x3d/0x50 kernel/locking/spinlock.c:170 
__run_hrtimer kernel/time/hrtimer.c:1781 [inline] 
__hrtimer_run_queues+0x5e2/0xc30 kernel/time/hrtimer.c:1841 
hrtimer_interrupt+0x45b/0xaa0 kernel/time/hrtimer.c:1903 
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1045 [inline] 
__sysvec_apic_timer_interrupt+0x102/0x3e0 arch/x86/kernel/apic/apic.c:1062 
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline] 
sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1056 
</IRQ> 
<TASK> 
asm_sysvec_apic_timer_interrupt+0x1a/0x20 
arch/x86/include/asm/idtentry.h:697 
RIP: 0010:deref_stack_reg+0x3/0x230 arch/x86/kernel/unwind_orc.c:418 
Code: e8 12 f8 b2 00 48 8b 4c 24 18 e9 f2 fe ff ff 0f 1f 84 00 00 00 00 00 
90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 55 41 57 <41> 56 41 55 41 
54 53 48 83 ec 20 48 89 54 24 18 49 89 f0 49 89 ff 
RSP: 0018:ffffc90002f16e00 EFLAGS: 00000283 
RAX: fffffffffffffff0 RBX: ffffffff9025420e RCX: 0000000000000000 
RDX: ffffc90002f16f28 RSI: ffffc90002f17ad0 RDI: ffffc90002f16ee8 
RBP: dffffc0000000000 R08: ffffc90002f16f47 R09: 0000000000000000 
R10: ffffc90002f16f38 R11: fffff520005e2de9 R12: ffffc90002f16f38 
R13: 1ffff920005e2ddf R14: ffffc90002f16ee8 R15: 1ffffffff204a842 
unwind_next_frame+0x18cc/0x23d0 arch/x86/kernel/unwind_orc.c:-1 
arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25 
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122 
kasan_save_stack mm/kasan/common.c:57 [inline] 
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78 
unpoison_slab_object mm/kasan/common.c:340 [inline] 
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366 
kasan_slab_alloc include/linux/kasan.h:253 [inline] 
slab_post_alloc_hook mm/slub.c:4953 [inline] 
slab_alloc_node mm/slub.c:5263 [inline] 
kmem_cache_alloc_noprof+0x37d/0x710 mm/slub.c:5270 
mt_alloc_one lib/maple_tree.c:174 [inline] 
mas_alloc_nodes+0x291/0x350 lib/maple_tree.c:1110 
mas_preallocate+0x2e0/0x670 lib/maple_tree.c:5194 
vma_iter_prealloc mm/vma.h:502 [inline] 
vma_shrink+0x18d/0x510 mm/vma.c:1200 
relocate_vma_down+0x4d4/0x4f0 mm/vma_exec.c:91 
setup_arg_pages+0x5cf/0xa90 fs/exec.c:690 
load_elf_binary+0xba4/0x2740 fs/binfmt_elf.c:1028 
search_binary_handler fs/exec.c:1669 [inline] 
exec_binprm fs/exec.c:1701 [inline] 
bprm_execve+0x92e/0x1400 fs/exec.c:1753 
do_execveat_common+0x510/0x6a0 fs/exec.c:1859 
do_execve fs/exec.c:1933 [inline] 
__do_sys_execve fs/exec.c:2009 [inline] 
__se_sys_execve fs/exec.c:2004 [inline] 
__x64_sys_execve+0x94/0xb0 fs/exec.c:2004 
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] 
do_syscall_64+0xec/0xf80 arch/x86/entry/syscall_64.c:94 
entry_SYSCALL_64_after_hwframe+0x77/0x7f 
RIP: 0033:0x7f94259c2e17 
Code: Unable to access opcode bytes at 0x7f94259c2ded. 
RSP: 002b:00007f9426807df8 EFLAGS: 00000206 ORIG_RAX: 000000000000003b 
RAX: ffffffffffffffda RBX: 00007ffd48e33ef5 RCX: 00007f94259c2e17 
RDX: 00007ffd48e32ba0 RSI: 00007ffd48e32de0 RDI: 00007ffd48e33ef5 
RBP: 00007f9426807e70 R08: 00007f9426807f20 R09: 0000000000000000 
R10: 0000000000000008 R11: 0000000000000206 R12: 00007ffd48e32de0 
R13: 00007ffd48e32ba0 R14: 0000000000000000 R15: 0000000000000000 
</TASK> 
rcu: rcu_preempt kthread starved for 10495 jiffies! g13757 f0x0 
RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0 
rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now 
expected behavior. 
rcu: RCU grace-period kthread stack dump: 
task:rcu_preempt state:R running task stack:27480 pid:16 tgid:16 ppid:2 
task_flags:0x208040 flags:0x00080000 
Call Trace: 
<TASK> 
context_switch kernel/sched/core.c:5256 [inline] 
__schedule+0x149b/0x4fd0 kernel/sched/core.c:6863 
__schedule_loop kernel/sched/core.c:6945 [inline] 
schedule+0x165/0x360 kernel/sched/core.c:6960 
schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99 
rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083 
rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285 
kthread+0x711/0x8a0 kernel/kthread.c:463 
ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158 
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 
</TASK> 
rcu: Stack dump where RCU GP kthread last ran: 
CPU: 0 UID: 0 PID: 5203 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS 
Google 10/25/2025 
RIP: 0010:csd_lock_wait kernel/smp.c:342 [inline] 
RIP: 0010:smp_call_function_many_cond+0xcc5/0x1260 kernel/smp.c:877 
Code: 45 8b 2c 24 44 89 ee 83 e6 01 31 ff e8 d4 97 0b 00 41 83 e5 01 49 bd 
00 00 00 00 00 fc ff df 75 07 e8 7f 93 0b 00 eb 38 f3 90 <42> 0f b6 04 2b 
84 c0 75 11 41 f7 04 24 01 00 00 00 74 1e e8 63 93 
RSP: 0000:ffffc90003057820 EFLAGS: 00000293 
RAX: ffffffff81b5654d RBX: 1ffff110170e8129 RCX: ffff88807d153d00 
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000 
RBP: ffffc90003057950 R08: ffffffff8f822e77 R09: 1ffffffff1f045ce 
R10: dffffc0000000000 R11: fffffbfff1f045cf R12: ffff8880b8740948 
R13: dffffc0000000000 R14: ffff8880b863bb00 R15: 0000000000000001 
FS: 00007f6e0f393880(0000) GS:ffff888125e1e000(0000) knlGS:0000000000000000 
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 
CR2: 000055ec54628550 CR3: 000000007d7b8000 CR4: 00000000003526f0 
Call Trace: 
<TASK> 
on_each_cpu_cond_mask+0x3f/0x80 kernel/smp.c:1043 
__flush_tlb_multi arch/x86/include/asm/paravirt.h:91 [inline] 
flush_tlb_multi arch/x86/mm/tlb.c:1382 [inline] 
flush_tlb_mm_range+0x60a/0x1170 arch/x86/mm/tlb.c:1472 
flush_tlb_page arch/x86/include/asm/tlbflush.h:324 [inline] 
ptep_clear_flush+0x120/0x170 mm/pgtable-generic.c:103 
wp_page_copy mm/memory.c:3785 [inline] 
do_wp_page+0x1bb1/0x5810 mm/memory.c:4180 
handle_pte_fault mm/memory.c:6289 [inline] 
__handle_mm_fault mm/memory.c:6411 [inline] 
handle_mm_fault+0x14c5/0x32b0 mm/memory.c:6580 
do_user_addr_fault+0xa7c/0x1380 arch/x86/mm/fault.c:1336 
handle_page_fault arch/x86/mm/fault.c:1476 [inline] 
exc_page_fault+0x71/0xd0 arch/x86/mm/fault.c:1532 
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618 
RIP: 0033:0x7f6e0ecb5dfe 
Code: 00 00 66 0f ef c0 41 0f 11 44 24 20 49 89 54 24 10 49 89 74 24 18 4c 
89 66 10 4c 89 62 18 48 89 c2 48 83 ca 01 49 89 54 24 08 <49> 89 04 04 48 
83 c4 10 5b 41 5c 41 5d c3 0f 1f 40 00 48 89 cf 48 
RSP: 002b:00007fff1a84f050 EFLAGS: 00010206 
RAX: 0000000000002a20 RBX: 0000000000000740 RCX: 000055ec54627e10 
RDX: 0000000000002a21 RSI: 00007f6e0edf1b20 RDI: 000055ec54627e10 
RBP: 00007f6e0edf1ac0 R08: 0000000000000740 R09: 0000000000000010 
R10: 000055ec24e255e0 R11: 0000000000000004 R12: 000055ec54625b30 
R13: 00007f6e0edf1ac0 R14: 0000000000000740 R15: 00007f6e0edf1ac0 
</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. 

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