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a89fac57b5
Lockdep warns about false positive:
[ 12.492084] 00000000e6b28347 (&head->lock){+...}, at: pcpu_freelist_push+0x2a/0x40
[ 12.492696] but this lock was taken by another, HARDIRQ-safe lock in the past:
[ 12.493275] (&rq->lock){-.-.}
[ 12.493276]
[ 12.493276]
[ 12.493276] and interrupts could create inverse lock ordering between them.
[ 12.493276]
[ 12.494435]
[ 12.494435] other info that might help us debug this:
[ 12.494979] Possible interrupt unsafe locking scenario:
[ 12.494979]
[ 12.495518] CPU0 CPU1
[ 12.495879] ---- ----
[ 12.496243] lock(&head->lock);
[ 12.496502] local_irq_disable();
[ 12.496969] lock(&rq->lock);
[ 12.497431] lock(&head->lock);
[ 12.497890] <Interrupt>
[ 12.498104] lock(&rq->lock);
[ 12.498368]
[ 12.498368] *** DEADLOCK ***
[ 12.498368]
[ 12.498837] 1 lock held by dd/276:
[ 12.499110] #0: 00000000c58cb2ee (rcu_read_lock){....}, at: trace_call_bpf+0x5e/0x240
[ 12.499747]
[ 12.499747] the shortest dependencies between 2nd lock and 1st lock:
[ 12.500389] -> (&rq->lock){-.-.} {
[ 12.500669] IN-HARDIRQ-W at:
[ 12.500934] _raw_spin_lock+0x2f/0x40
[ 12.501373] scheduler_tick+0x4c/0xf0
[ 12.501812] update_process_times+0x40/0x50
[ 12.502294] tick_periodic+0x27/0xb0
[ 12.502723] tick_handle_periodic+0x1f/0x60
[ 12.503203] timer_interrupt+0x11/0x20
[ 12.503651] __handle_irq_event_percpu+0x43/0x2c0
[ 12.504167] handle_irq_event_percpu+0x20/0x50
[ 12.504674] handle_irq_event+0x37/0x60
[ 12.505139] handle_level_irq+0xa7/0x120
[ 12.505601] handle_irq+0xa1/0x150
[ 12.506018] do_IRQ+0x77/0x140
[ 12.506411] ret_from_intr+0x0/0x1d
[ 12.506834] _raw_spin_unlock_irqrestore+0x53/0x60
[ 12.507362] __setup_irq+0x481/0x730
[ 12.507789] setup_irq+0x49/0x80
[ 12.508195] hpet_time_init+0x21/0x32
[ 12.508644] x86_late_time_init+0xb/0x16
[ 12.509106] start_kernel+0x390/0x42a
[ 12.509554] secondary_startup_64+0xa4/0xb0
[ 12.510034] IN-SOFTIRQ-W at:
[ 12.510305] _raw_spin_lock+0x2f/0x40
[ 12.510772] try_to_wake_up+0x1c7/0x4e0
[ 12.511220] swake_up_locked+0x20/0x40
[ 12.511657] swake_up_one+0x1a/0x30
[ 12.512070] rcu_process_callbacks+0xc5/0x650
[ 12.512553] __do_softirq+0xe6/0x47b
[ 12.512978] irq_exit+0xc3/0xd0
[ 12.513372] smp_apic_timer_interrupt+0xa9/0x250
[ 12.513876] apic_timer_interrupt+0xf/0x20
[ 12.514343] default_idle+0x1c/0x170
[ 12.514765] do_idle+0x199/0x240
[ 12.515159] cpu_startup_entry+0x19/0x20
[ 12.515614] start_kernel+0x422/0x42a
[ 12.516045] secondary_startup_64+0xa4/0xb0
[ 12.516521] INITIAL USE at:
[ 12.516774] _raw_spin_lock_irqsave+0x38/0x50
[ 12.517258] rq_attach_root+0x16/0xd0
[ 12.517685] sched_init+0x2f2/0x3eb
[ 12.518096] start_kernel+0x1fb/0x42a
[ 12.518525] secondary_startup_64+0xa4/0xb0
[ 12.518986] }
[ 12.519132] ... key at: [<ffffffff82b7bc28>] __key.71384+0x0/0x8
[ 12.519649] ... acquired at:
[ 12.519892] pcpu_freelist_pop+0x7b/0xd0
[ 12.520221] bpf_get_stackid+0x1d2/0x4d0
[ 12.520563] ___bpf_prog_run+0x8b4/0x11a0
[ 12.520887]
[ 12.521008] -> (&head->lock){+...} {
[ 12.521292] HARDIRQ-ON-W at:
[ 12.521539] _raw_spin_lock+0x2f/0x40
[ 12.521950] pcpu_freelist_push+0x2a/0x40
[ 12.522396] bpf_get_stackid+0x494/0x4d0
[ 12.522828] ___bpf_prog_run+0x8b4/0x11a0
[ 12.523296] INITIAL USE at:
[ 12.523537] _raw_spin_lock+0x2f/0x40
[ 12.523944] pcpu_freelist_populate+0xc0/0x120
[ 12.524417] htab_map_alloc+0x405/0x500
[ 12.524835] __do_sys_bpf+0x1a3/0x1a90
[ 12.525253] do_syscall_64+0x4a/0x180
[ 12.525659] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 12.526167] }
[ 12.526311] ... key at: [<ffffffff838f7668>] __key.13130+0x0/0x8
[ 12.526812] ... acquired at:
[ 12.527047] __lock_acquire+0x521/0x1350
[ 12.527371] lock_acquire+0x98/0x190
[ 12.527680] _raw_spin_lock+0x2f/0x40
[ 12.527994] pcpu_freelist_push+0x2a/0x40
[ 12.528325] bpf_get_stackid+0x494/0x4d0
[ 12.528645] ___bpf_prog_run+0x8b4/0x11a0
[ 12.528970]
[ 12.529092]
[ 12.529092] stack backtrace:
[ 12.529444] CPU: 0 PID: 276 Comm: dd Not tainted 5.0.0-rc3-00018-g2fa53f892422 #475
[ 12.530043] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014
[ 12.530750] Call Trace:
[ 12.530948] dump_stack+0x5f/0x8b
[ 12.531248] check_usage_backwards+0x10c/0x120
[ 12.531598] ? ___bpf_prog_run+0x8b4/0x11a0
[ 12.531935] ? mark_lock+0x382/0x560
[ 12.532229] mark_lock+0x382/0x560
[ 12.532496] ? print_shortest_lock_dependencies+0x180/0x180
[ 12.532928] __lock_acquire+0x521/0x1350
[ 12.533271] ? find_get_entry+0x17f/0x2e0
[ 12.533586] ? find_get_entry+0x19c/0x2e0
[ 12.533902] ? lock_acquire+0x98/0x190
[ 12.534196] lock_acquire+0x98/0x190
[ 12.534482] ? pcpu_freelist_push+0x2a/0x40
[ 12.534810] _raw_spin_lock+0x2f/0x40
[ 12.535099] ? pcpu_freelist_push+0x2a/0x40
[ 12.535432] pcpu_freelist_push+0x2a/0x40
[ 12.535750] bpf_get_stackid+0x494/0x4d0
[ 12.536062] ___bpf_prog_run+0x8b4/0x11a0
It has been explained that is a false positive here:
https://lkml.org/lkml/2018/7/25/756
Recap:
- stackmap uses pcpu_freelist
- The lock in pcpu_freelist is a percpu lock
- stackmap is only used by tracing bpf_prog
- A tracing bpf_prog cannot be run if another bpf_prog
has already been running (ensured by the percpu bpf_prog_active counter).
Eric pointed out that this lockdep splats stops other
legit lockdep splats in selftests/bpf/test_progs.c.
Fix this by calling local_irq_save/restore for stackmap.
Another false positive had also been worked around by calling
local_irq_save in commit
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