On Mon, Aug 05 2024 at 00:53, syzbot wrote: Cc+ wireless folks. > Hello, > > syzbot found the following issue on: > > HEAD commit: 3d650ab5e7d9 selftests/bpf: Fix a btf_dump selftest failure > git tree: bpf-next > console output: https://syzkaller.appspot.com/x/log.txt?x=17e154d3980000 > kernel config: https://syzkaller.appspot.com/x/.config?x=5efb917b1462a973 > dashboard link: https://syzkaller.appspot.com/bug?extid=41e4341f493f1155aa3d > 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/630e210de8d9/disk-3d650ab5.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/3576ca35748a/vmlinux-3d650ab5.xz > kernel image: https://storage.googleapis.com/syzbot-assets/5b33f099abfa/bzImage-3d650ab5.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+41e4341f493f1155aa3d@xxxxxxxxxxxxxxxxxxxxxxxxx > > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 11474 at kernel/time/hrtimer.c:1048 hrtimer_forward+0x210/0x2d0 kernel/time/hrtimer.c:1048 That tries to forward a hrtimer which is currently enqueued. > Modules linked in: > CPU: 0 UID: 0 PID: 11474 Comm: syz.2.2194 Not tainted 6.10.0-syzkaller-12666-g3d650ab5e7d9 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024 > RIP: 0010:hrtimer_forward+0x210/0x2d0 kernel/time/hrtimer.c:1048 > Code: 00 49 89 1e 48 8b 04 24 eb 07 e8 bb e7 12 00 31 c0 48 83 c4 30 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc e8 a1 e7 12 00 90 <0f> 0b 90 eb e0 4c 89 f0 31 d2 49 f7 f4 48 89 04 24 49 89 c6 4d 0f > RSP: 0018:ffffc90000007bf8 EFLAGS: 00010246 > RAX: ffffffff81809d7f RBX: 0000000000000001 RCX: ffff888026059e00 > RDX: 0000000000000101 RSI: 0000000000000001 RDI: 0000000000000000 > RBP: 00000042facd7bc5 R08: ffffffff81809c13 R09: 1ffffffff26e4d1f > R10: dffffc0000000000 R11: ffffffff81358260 R12: 00000000061a8000 > R13: ffff88807db07080 R14: 000000000044e132 R15: 1ffff1100fb60e0c > FS: 00007fa65d4636c0(0000) GS:ffff8880b9200000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f478b2356c0 CR3: 000000005beac000 CR4: 00000000003506f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600 > Call Trace: > <IRQ> > hrtimer_forward_now include/linux/hrtimer.h:355 [inline] > mac80211_hwsim_beacon+0x192/0x1f0 drivers/net/wireless/virtual/mac80211_hwsim.c:2354 This is the timer callback. So something has re-started the timer before the soft interrupt was able to run .... > __run_hrtimer kernel/time/hrtimer.c:1689 [inline] > __hrtimer_run_queues+0x59b/0xd50 kernel/time/hrtimer.c:1753 > hrtimer_run_softirq+0x19a/0x2c0 kernel/time/hrtimer.c:1770 > handle_softirqs+0x2c4/0x970 kernel/softirq.c:554 > __do_softirq kernel/softirq.c:588 [inline] > invoke_softirq kernel/softirq.c:428 [inline] > __irq_exit_rcu+0xf4/0x1c0 kernel/softirq.c:637 > irq_exit_rcu+0x9/0x30 kernel/softirq.c:649 > instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline] > sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1043 > </IRQ> > <TASK> > asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702 mac80211_hwsim_link_info_changed() and mac80211_hwsim_config() can re-start the timer concurrently to a running softirq callback. I can't see any serialization there. The check for hrtimer_queued() is not cutting it as that's a lockless check and becomes true when the timer is dequeued for expiry. So the following can happen: CPU0 CPU1 hrtimer_softirq() lock_base(); dequeue_timer(t); base->running = t; unlock_base(t); if (!hrtimer_queued(t)) t->fn(t) hrtimer_start(t); .... hrtimer_forward(t); <- FAIL Replacing hrtimer_queued() with hrtimer_active() should solve the hrtimer race, but I wonder whether the concurrency between the soft interrupt and the config/info changes has other side effects. Thanks, tglx
