[syzbot] [fuse?] BUG: scheduling while atomic in __synchronize_srcu

[syzbot] [fuse?] BUG: scheduling while atomic in __synchronize_srcu

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    7f87a5ea75f0 Merge tag 'hid-for-linus-2026040801' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12439316580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2d08886358f27e8c
dashboard link: https://syzkaller.appspot.com/bug?extid=12b178b7c756664d2518
compiler:       aarch64-linux-gnu-gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1461aeba580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14c85e06580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/fa3fbcfdac58/non_bootable_disk-7f87a5ea.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/28f02ff1720d/vmlinux-7f87a5ea.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7d30b9e8505e/Image-7f87a5ea.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+12b178b7c756664d2518@syzkaller.appspotmail.com

BUG: scheduling while atomic: syz.1.49/3699/0x00000002
Modules linked in:
CPU: 1 UID: 0 PID: 3699 Comm: syz.1.49 Not tainted syzkaller #0 PREEMPT 
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace arch/arm64/kernel/stacktrace.c:498 [inline] (C)
 show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x60/0x80 lib/dump_stack.c:120
 dump_stack+0x18/0x24 lib/dump_stack.c:129
 __schedule_bug+0x54/0x78 kernel/sched/core.c:5847
 schedule_debug kernel/sched/core.c:5874 [inline]
 __schedule+0x858/0xd84 kernel/sched/core.c:6786
 __schedule_loop kernel/sched/core.c:6993 [inline]
 schedule+0x34/0x114 kernel/sched/core.c:7008
 schedule_timeout+0xd4/0x110 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x78/0x160 kernel/sched/completion.c:153
 __synchronize_srcu+0x90/0xd0 kernel/rcu/srcutree.c:1496
 synchronize_srcu_expedited+0x24/0x40 kernel/rcu/srcutree.c:1521
 kvm_set_irq_routing+0x204/0x294 virt/kvm/irqchip.c:225
 kvm_vgic_setup_default_irq_routing+0x78/0xc0 arch/arm64/kvm/vgic/vgic-irqfd.c:153
 vgic_init+0x1ac/0x268 arch/arm64/kvm/vgic/vgic-init.c:421
 vgic_lazy_init+0x54/0x6c arch/arm64/kvm/vgic/vgic-init.c:550
 kvm_vgic_inject_irq+0x30/0x12c arch/arm64/kvm/vgic/vgic.c:520
 kvm_timer_update_irq+0x68/0x7c arch/arm64/kvm/arch_timer.c:450
 kvm_timer_vcpu_reset+0xd8/0x1e0 arch/arm64/kvm/arch_timer.c:1036
 kvm_reset_vcpu+0x194/0x360 arch/arm64/kvm/reset.c:268
 kvm_vcpu_set_target arch/arm64/kvm/arm.c:1632 [inline]
 kvm_arch_vcpu_ioctl_vcpu_init arch/arm64/kvm/arm.c:1652 [inline]
 kvm_arch_vcpu_ioctl+0x2e4/0x8c8 arch/arm64/kvm/arm.c:1773
 kvm_vcpu_ioctl+0x4ac/0x8f4 virt/kvm/kvm_main.c:4653
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __arm64_sys_ioctl+0xac/0x104 fs/ioctl.c:583
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x48/0x104 arch/arm64/kernel/syscall.c:49
 el0_svc_common.constprop.0+0x40/0xe0 arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x1c/0x28 arch/arm64/kernel/syscall.c:151
 el0_svc+0x34/0x124 arch/arm64/kernel/entry-common.c:724
 el0t_64_sync_handler+0xa0/0xf0 arch/arm64/kernel/entry-common.c:743
 el0t_64_sync+0x1a4/0x1a8 arch/arm64/kernel/entry.S:596
BUG: scheduling while atomic: syz.1.49/3699/0x00000000
Modules linked in:
CPU: 1 UID: 0 PID: 3699 Comm: syz.1.49 Tainted: G        W           syzkaller #0 PREEMPT 
Tainted: [W]=WARN
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace arch/arm64/kernel/stacktrace.c:498 [inline] (C)
 show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x60/0x80 lib/dump_stack.c:120
 dump_stack+0x18/0x24 lib/dump_stack.c:129
 __schedule_bug+0x54/0x78 kernel/sched/core.c:5847
 schedule_debug kernel/sched/core.c:5874 [inline]
 __schedule+0x858/0xd84 kernel/sched/core.c:6786
 __schedule_loop kernel/sched/core.c:6993 [inline]
 schedule+0x34/0x114 kernel/sched/core.c:7008
 futex_do_wait kernel/futex/waitwake.c:358 [inline]
 __futex_wait+0xf0/0x178 kernel/futex/waitwake.c:687
 futex_wait+0x88/0x118 kernel/futex/waitwake.c:715
 do_futex+0xf8/0x1a0 kernel/futex/syscalls.c:130
 __do_sys_futex kernel/futex/syscalls.c:207 [inline]
 __se_sys_futex kernel/futex/syscalls.c:188 [inline]
 __arm64_sys_futex+0xfc/0x1a0 kernel/futex/syscalls.c:188
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x48/0x104 arch/arm64/kernel/syscall.c:49
 el0_svc_common.constprop.0+0x40/0xe0 arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x1c/0x28 arch/arm64/kernel/syscall.c:151
 el0_svc+0x34/0x124 arch/arm64/kernel/entry-common.c:724
 el0t_64_sync_handler+0xa0/0xf0 arch/arm64/kernel/entry-common.c:743
 el0t_64_sync+0x1a4/0x1a8 arch/arm64/kernel/entry.S:596
psi: inconsistent task state! task=30:pr/ttyAMA-1 cpu=1 psi_flags=14 clear=0 set=10


---
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Forwarded: [PATCH] arm64: KVM: Initialize vGIC before preempt-disabled section in kvm_reset_vcpu()

[syzbot]

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***

Subject: [PATCH] arm64: KVM: Initialize vGIC before preempt-disabled section in kvm_reset_vcpu()
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


kvm_reset_vcpu() calls kvm_timer_vcpu_reset() inside a preempt-disabled
section to avoid races with preempt notifiers that also call vcpu put/load.

However, kvm_timer_vcpu_reset() eventually calls kvm_vgic_inject_irq()
which triggers vgic_lazy_init() if the vGIC has not been initialized yet.
vgic_lazy_init() acquires a mutex and calls vgic_init() which invokes
synchronize_srcu_expedited() -- both of which may sleep. Sleeping inside
a preempt-disabled section is illegal and causes:

  BUG: scheduling while atomic: syz.1.49/3699/0x00000002

Fix this by calling vgic_lazy_init() before preempt_disable(). On the
second call inside kvm_vgic_inject_irq(), vgic_initialized() will return
true and vgic_lazy_init() will return immediately without sleeping.

Reported-by: syzbot+12b178b7c756664d2518@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=12b178b7c756664d2518
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 arch/arm64/kvm/reset.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index b963fd975aac..4ee16b4a37b5 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -25,6 +25,7 @@
 #include <asm/ptrace.h>
 #include <asm/kvm_arm.h>
 #include <asm/kvm_asm.h>
+#include "vgic/vgic.h"
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_mmu.h>
 #include <asm/kvm_nested.h>
@@ -198,6 +199,14 @@ void kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 	vcpu->arch.reset_state.reset = false;
 	spin_unlock(&vcpu->arch.mp_state_lock);
 
+
+	/*
+	 * Initialize vGIC before entering preempt-disabled section.
+	 * vgic_lazy_init() may sleep via mutex_lock, which is illegal
+	 * inside preempt_disable(). Second call inside kvm_vgic_inject_irq
+	 * will find vGIC already initialized and return immediately.
+	 */
+	vgic_lazy_init(vcpu->kvm);
 	preempt_disable();
 	loaded = (vcpu->cpu != -1);
 	if (loaded)
-- 
2.43.0