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Recent improvements in LOCKDEP highlighted a potential A-A deadlock with
pcpu_freelist in NMI:
./tools/testing/selftests/bpf/test_progs -t stacktrace_build_id_nmi
[ 18.984807] ================================
[ 18.984807] WARNING: inconsistent lock state
[ 18.984808] 5.9.0-rc6-01771-g1466de1330e1 #2967 Not tainted
[ 18.984809] --------------------------------
[ 18.984809] inconsistent {INITIAL USE} -> {IN-NMI} usage.
[ 18.984810] test_progs/1990 [HC2[2]:SC0[0]:HE0:SE1] takes:
[ 18.984810] ffffe8ffffc219c0 (&head->lock){....}-{2:2}, at: __pcpu_freelist_pop+0xe3/0x180
[ 18.984813] {INITIAL USE} state was registered at:
[ 18.984814] lock_acquire+0x175/0x7c0
[ 18.984814] _raw_spin_lock+0x2c/0x40
[ 18.984815] __pcpu_freelist_pop+0xe3/0x180
[ 18.984815] pcpu_freelist_pop+0x31/0x40
[ 18.984816] htab_map_alloc+0xbbf/0xf40
[ 18.984816] __do_sys_bpf+0x5aa/0x3ed0
[ 18.984817] do_syscall_64+0x2d/0x40
[ 18.984818] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 18.984818] irq event stamp: 12
[...]
[ 18.984822] other info that might help us debug this:
[ 18.984823] Possible unsafe locking scenario:
[ 18.984823]
[ 18.984824] CPU0
[ 18.984824] ----
[ 18.984824] lock(&head->lock);
[ 18.984826] <Interrupt>
[ 18.984826] lock(&head->lock);
[ 18.984827]
[ 18.984828] *** DEADLOCK ***
[ 18.984828]
[ 18.984829] 2 locks held by test_progs/1990:
[...]
[ 18.984838] <NMI>
[ 18.984838] dump_stack+0x9a/0xd0
[ 18.984839] lock_acquire+0x5c9/0x7c0
[ 18.984839] ? lock_release+0x6f0/0x6f0
[ 18.984840] ? __pcpu_freelist_pop+0xe3/0x180
[ 18.984840] _raw_spin_lock+0x2c/0x40
[ 18.984841] ? __pcpu_freelist_pop+0xe3/0x180
[ 18.984841] __pcpu_freelist_pop+0xe3/0x180
[ 18.984842] pcpu_freelist_pop+0x17/0x40
[ 18.984842] ? lock_release+0x6f0/0x6f0
[ 18.984843] __bpf_get_stackid+0x534/0xaf0
[ 18.984843] bpf_prog_1fd9e30e1438d3c5_oncpu+0x73/0x350
[ 18.984844] bpf_overflow_handler+0x12f/0x3f0
This is because pcpu_freelist_head.lock is accessed in both NMI and
non-NMI context. Fix this issue by using raw_spin_trylock() in NMI.
Since NMI interrupts non-NMI context, when NMI context tries to lock the
raw_spinlock, non-NMI context of the same CPU may already have locked a
lock and is blocked from unlocking the lock. For a system with N CPUs,
there could be N NMIs at the same time, and they may block N non-NMI
raw_spinlocks. This is tricky for pcpu_freelist_push(), where unlike
_pop(), failing _push() means leaking memory. This issue is more likely to
trigger in non-SMP system.
Fix this issue with an extra list, pcpu_freelist.extralist. The extralist
is primarily used to take _push() when raw_spin_trylock() failed on all
the per CPU lists. It should be empty most of the time. The following
table summarizes the behavior of pcpu_freelist in NMI and non-NMI:
non-NMI pop(): use _lock(); check per CPU lists first;
if all per CPU lists are empty, check extralist;
if extralist is empty, return NULL.
non-NMI push(): use _lock(); only push to per CPU lists.
NMI pop(): use _trylock(); check per CPU lists first;
if all per CPU lists are locked or empty, check extralist;
if extralist is locked or empty, return NULL.
NMI push(): use _trylock(); check per CPU lists first;
if all per CPU lists are locked; try push to extralist;
if extralist is also locked, keep trying on per CPU lists.
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20201005165838.3735218-1-songliubraving@fb.com
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Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of version 2 of the gnu general public license as
published by the free software foundation
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 107 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Richard Fontana <rfontana@redhat.com>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190528171438.615055994@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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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 89ad2fa3f043 ("bpf: fix lockdep splat").
That commit added unnecessary irq_save/restore to fast path of
bpf hash map. irqs are already disabled at that point, since htab
is holding per bucket spin_lock with irqsave.
Let's reduce overhead for htab by introducing __pcpu_freelist_push/pop
function w/o irqsave and convert pcpu_freelist_push/pop to irqsave
to be used elsewhere (right now only in stackmap).
It stops lockdep false positive in stackmap with a bit of acceptable overhead.
Fixes: 557c0c6e7df8 ("bpf: convert stackmap to pre-allocation")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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Introduce simple percpu_freelist to keep single list of elements
spread across per-cpu singly linked lists.
/* push element into the list */
void pcpu_freelist_push(struct pcpu_freelist *, struct pcpu_freelist_node *);
/* pop element from the list */
struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *);
The object is pushed to the current cpu list.
Pop first trying to get the object from the current cpu list,
if it's empty goes to the neigbour cpu list.
For bpf program usage pattern the collision rate is very low,
since programs push and pop the objects typically on the same cpu.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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