[syzbot] [kernel?] KMSAN: uninit-value in __flush_smp_call_function_queue

[syzbot] [kernel?] KMSAN: uninit-value in __flush_smp_call_function_queue

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    ca4ee40bf13d Partly revert "drm/hyperv: Remove reference t..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=114ac722580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4b4f2aab682301f1
dashboard link: https://syzkaller.appspot.com/bug?extid=4b1bd55fba6260160779
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/68f5e4558a91/disk-ca4ee40b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ea1eab60444d/vmlinux-ca4ee40b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cc7e3debdec4/bzImage-ca4ee40b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4b1bd55fba6260160779@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in __flush_smp_call_function_queue+0x362/0x18e0 kernel/smp.c:535
 __flush_smp_call_function_queue+0x362/0x18e0 kernel/smp.c:535
 generic_smp_call_function_single_interrupt+0x1c/0x30 kernel/smp.c:463
 __sysvec_call_function_single+0x4b/0x3e0 arch/x86/kernel/smp.c:271
 instr_sysvec_call_function_single arch/x86/kernel/smp.c:266 [inline]
 sysvec_call_function_single+0x7c/0x90 arch/x86/kernel/smp.c:266
 asm_sysvec_call_function_single+0x1f/0x30 arch/x86/include/asm/idtentry.h:704
 kmsan_get_metadata+0x12e/0x160 mm/kmsan/shadow.c:148
 kmsan_get_shadow_origin_ptr+0x35/0xb0 mm/kmsan/shadow.c:97
 get_shadow_origin_ptr mm/kmsan/instrumentation.c:38 [inline]
 __msan_metadata_ptr_for_load_8+0x24/0x40 mm/kmsan/instrumentation.c:94
 on_stack+0x5f/0x1f0 arch/x86/include/asm/stacktrace.h:56
 update_stack_state+0xa7/0x1c0 arch/x86/kernel/unwind_frame.c:228
 unwind_next_frame+0x116/0x350 arch/x86/kernel/unwind_frame.c:315
 arch_stack_walk+0x1b0/0x280 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xc2/0x100 kernel/stacktrace.c:122
 ref_tracker_alloc+0x1b2/0x7a0 lib/ref_tracker.c:277
 __netdev_tracker_alloc include/linux/netdevice.h:4403 [inline]
 netdev_tracker_alloc include/linux/netdevice.h:4415 [inline]
 netdev_get_by_index+0xf6/0x1b0 net/core/dev.c:1020
 fib6_nh_init+0x172/0x32c0 net/ipv6/route.c:3600
 ip6_route_info_create_nh+0x4e4/0xf60 net/ipv6/route.c:3900
 ip6_route_add+0x159/0x4a0 net/ipv6/route.c:3952
 addrconf_add_mroute net/ipv6/addrconf.c:2552 [inline]
 addrconf_add_dev+0x6af/0x790 net/ipv6/addrconf.c:2570
 inet6_addr_add+0x2d5/0x1570 net/ipv6/addrconf.c:3032
 inet6_rtm_newaddr+0x1a0f/0x1dd0 net/ipv6/addrconf.c:5064
 rtnetlink_rcv_msg+0x106f/0x14b0 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x54d/0x680 net/netlink/af_netlink.c:2550
 rtnetlink_rcv+0x35/0x40 net/core/rtnetlink.c:6985
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0xf04/0x12b0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x10b2/0x1250 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg net/socket.c:742 [inline]
 __sys_sendto+0xa77/0xb90 net/socket.c:2206
 __do_sys_sendto net/socket.c:2213 [inline]
 __se_sys_sendto net/socket.c:2209 [inline]
 __x64_sys_sendto+0x130/0x200 net/socket.c:2209
 x64_sys_call+0x39a0/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:45
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable prefix created at:
 record_print_text+0xca/0x8e0 kernel/printk/printk.c:1420
 printk_get_next_message+0xc7c/0x1250 kernel/printk/printk.c:3072

CPU: 0 UID: 0 PID: 15335 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================


---
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Re: [syzbot] [kernel?] KMSAN: uninit-value in __flush_smp_call_function_queue

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    ca4ee40bf13d Partly revert "drm/hyperv: Remove reference t..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=177aec02580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4b4f2aab682301f1
dashboard link: https://syzkaller.appspot.com/bug?extid=4b1bd55fba6260160779
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120fc722580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10faec02580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/68f5e4558a91/disk-ca4ee40b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ea1eab60444d/vmlinux-ca4ee40b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cc7e3debdec4/bzImage-ca4ee40b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4b1bd55fba6260160779@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in __flush_smp_call_function_queue+0x362/0x18e0 kernel/smp.c:535
 __flush_smp_call_function_queue+0x362/0x18e0 kernel/smp.c:535
 generic_smp_call_function_single_interrupt+0x1c/0x30 kernel/smp.c:463
 __sysvec_call_function_single+0x4b/0x3e0 arch/x86/kernel/smp.c:271
 instr_sysvec_call_function_single arch/x86/kernel/smp.c:266 [inline]
 sysvec_call_function_single+0x7c/0x90 arch/x86/kernel/smp.c:266
 asm_sysvec_call_function_single+0x1f/0x30 arch/x86/include/asm/idtentry.h:704
 native_irq_enable arch/x86/include/asm/irqflags.h:42 [inline]
 arch_local_irq_enable arch/x86/include/asm/irqflags.h:119 [inline]
 raw_spin_rq_unlock_irq kernel/sched/sched.h:1629 [inline]
 finish_lock_switch kernel/sched/core.c:5032 [inline]
 finish_task_switch+0x11b/0x8b0 kernel/sched/core.c:5150
 context_switch kernel/sched/core.c:5298 [inline]
 __schedule+0x273e/0x8650 kernel/sched/core.c:6907
 schedule_idle+0x5a/0x90 kernel/sched/core.c:7030
 do_idle+0x748/0x760 kernel/sched/idle.c:360
 cpu_startup_entry+0x5f/0x80 kernel/sched/idle.c:430
 start_secondary+0xcc/0xd0 arch/x86/kernel/smpboot.c:312
 common_startup_64+0x13e/0x147

Local variable reuse.i created at:
 mas_wr_node_store lib/maple_tree.c:3495 [inline]
 mas_wr_store_entry+0x14bd/0x96d0 lib/maple_tree.c:3764
 mas_store_prealloc+0x1834/0x1e60 lib/maple_tree.c:5169

CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================


---
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] [kernel?] KMSAN: uninit-value in __flush_smp_call_function_queue

[Qing Wang]

#syz test

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 5aa4c9500018..0aecb4d523cd 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3492,7 +3492,7 @@ static inline void mas_wr_node_store(struct ma_wr_state *wr_mas,
 	void __rcu **dst_slots;
 	unsigned long *dst_pivots;
 	unsigned char dst_offset, offset_end = wr_mas->offset_end;
-	struct maple_node reuse, *newnode;
+	struct maple_node reuse = {0}, *newnode;
 	unsigned char copy_size, node_pivots = mt_pivots[wr_mas->type];
 	bool in_rcu = mt_in_rcu(mas->tree);
 	unsigned char height = mas_mt_height(mas);

Re: [syzbot] [kernel?] KMSAN: uninit-value in __flush_smp_call_function_queue

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KMSAN: uninit-value in __flush_smp_call_function_queue

=====================================================
BUG: KMSAN: uninit-value in __flush_smp_call_function_queue+0x362/0x18e0 kernel/smp.c:535
 __flush_smp_call_function_queue+0x362/0x18e0 kernel/smp.c:535
 generic_smp_call_function_single_interrupt+0x1c/0x30 kernel/smp.c:463
 __sysvec_call_function_single+0x4b/0x3e0 arch/x86/kernel/smp.c:271
 instr_sysvec_call_function_single arch/x86/kernel/smp.c:266 [inline]
 sysvec_call_function_single+0x7c/0x90 arch/x86/kernel/smp.c:266
 asm_sysvec_call_function_single+0x1f/0x30 arch/x86/include/asm/idtentry.h:704
 native_irq_enable arch/x86/include/asm/irqflags.h:42 [inline]
 arch_local_irq_enable arch/x86/include/asm/irqflags.h:119 [inline]
 raw_spin_rq_unlock_irq kernel/sched/sched.h:1629 [inline]
 finish_lock_switch kernel/sched/core.c:5032 [inline]
 finish_task_switch+0x11b/0x8b0 kernel/sched/core.c:5150
 context_switch kernel/sched/core.c:5298 [inline]
 __schedule+0x2607/0x8640 kernel/sched/core.c:6908
 preempt_schedule_common+0x33/0x80 kernel/sched/core.c:7092
 preempt_schedule+0x30/0x40 kernel/sched/core.c:7116
 preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:179 [inline]
 _raw_spin_unlock_irqrestore+0x57/0x60 kernel/locking/spinlock.c:194
 unlock_hrtimer_base kernel/time/hrtimer.c:1021 [inline]
 hrtimer_try_to_cancel+0x8b0/0xae0 kernel/time/hrtimer.c:1368
 hrtimer_cancel+0x33/0xf0 kernel/time/hrtimer.c:1489
 schedule_hrtimeout_range_clock+0x16d/0x2f0 kernel/time/sleep_timeout.c:218
 schedule_hrtimeout_range+0x42/0x50 kernel/time/sleep_timeout.c:263
 poll_schedule_timeout fs/select.c:241 [inline]
 do_select+0x282b/0x2aa0 fs/select.c:603
 core_sys_select+0xa5a/0x10e0 fs/select.c:677
 do_pselect fs/select.c:759 [inline]
 __do_sys_pselect6 fs/select.c:798 [inline]
 __se_sys_pselect6+0x554/0x6b0 fs/select.c:789
 __x64_sys_pselect6+0x114/0x1a0 fs/select.c:789
 x64_sys_call+0xa5d/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:271
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable mmap_event created at:
 perf_event_mmap+0x47/0x2fe0 kernel/events/core.c:9894
 __mmap_complete mm/vma.c:2585 [inline]
 __mmap_region mm/vma.c:2768 [inline]
 mmap_region+0x4a79/0x6220 mm/vma.c:2837

CPU: 1 UID: 0 PID: 6279 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================


Tested on:

commit:         1f318b96 Linux 7.0-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d4694a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=242f02fcd3fbc8f3
dashboard link: https://syzkaller.appspot.com/bug?extid=4b1bd55fba6260160779
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=1227175a580000