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Commit dcab2483 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Greg Kroah-Hartman
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bpf: fix lockdep false positive in percpu_freelist 

[ Upstream commit a89fac57 ]

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-g2fa53f89 #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 89ad2fa3 ("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: 557c0c6e ("bpf: convert stackmap to pre-allocation")
Reported-by: default avatarNaresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 3084058a
Hide whitespace changes
Inline Side-by-side
Showing with 35 additions and 14 deletions
kernel/bpf/hashtab.c
View file @ dcab2483
......@@ -655,7 +655,7 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
}
if (htab_is_prealloc(htab)) {
pcpu_freelist_push(&htab->freelist, &l->fnode);
__pcpu_freelist_push(&htab->freelist, &l->fnode);
} else {
atomic_dec(&htab->count);
l->htab = htab;
......@@ -717,7 +717,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
} else {
struct pcpu_freelist_node *l;
l = pcpu_freelist_pop(&htab->freelist);
l = __pcpu_freelist_pop(&htab->freelist);
if (!l)
return ERR_PTR(-E2BIG);
l_new = container_of(l, struct htab_elem, fnode);
......
kernel/bpf/percpu_freelist.c
View file @ dcab2483
......@@ -28,8 +28,8 @@ void pcpu_freelist_destroy(struct pcpu_freelist *s)
free_percpu(s->freelist);
}
static inline void __pcpu_freelist_push(struct pcpu_freelist_head *head,
struct pcpu_freelist_node *node)
static inline void ___pcpu_freelist_push(struct pcpu_freelist_head *head,
struct pcpu_freelist_node *node)
{
raw_spin_lock(&head->lock);
node->next = head->first;
......@@ -37,12 +37,22 @@ static inline void __pcpu_freelist_push(struct pcpu_freelist_head *head,
raw_spin_unlock(&head->lock);
}
void pcpu_freelist_push(struct pcpu_freelist *s,
void __pcpu_freelist_push(struct pcpu_freelist *s,
struct pcpu_freelist_node *node)
{
struct pcpu_freelist_head *head = this_cpu_ptr(s->freelist);
__pcpu_freelist_push(head, node);
___pcpu_freelist_push(head, node);
}
void pcpu_freelist_push(struct pcpu_freelist *s,
struct pcpu_freelist_node *node)
{
unsigned long flags;
local_irq_save(flags);
__pcpu_freelist_push(s, node);
local_irq_restore(flags);
}
void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
......@@ -63,7 +73,7 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
for_each_possible_cpu(cpu) {
again:
head = per_cpu_ptr(s->freelist, cpu);
__pcpu_freelist_push(head, buf);
___pcpu_freelist_push(head, buf);
i++;
buf += elem_size;
if (i == nr_elems)
......@@ -74,14 +84,12 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
local_irq_restore(flags);
}
struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
struct pcpu_freelist_node *__pcpu_freelist_pop(struct pcpu_freelist *s)
{
struct pcpu_freelist_head *head;
struct pcpu_freelist_node *node;
unsigned long flags;
int orig_cpu, cpu;
local_irq_save(flags);
orig_cpu = cpu = raw_smp_processor_id();
while (1) {
head = per_cpu_ptr(s->freelist, cpu);
......@@ -89,16 +97,25 @@ struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
node = head->first;
if (node) {
head->first = node->next;
raw_spin_unlock_irqrestore(&head->lock, flags);
raw_spin_unlock(&head->lock);
return node;
}
raw_spin_unlock(&head->lock);
cpu = cpumask_next(cpu, cpu_possible_mask);
if (cpu >= nr_cpu_ids)
cpu = 0;
if (cpu == orig_cpu) {
local_irq_restore(flags);
if (cpu == orig_cpu)
return NULL;
}
}
}
struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *s)
{
struct pcpu_freelist_node *ret;
unsigned long flags;
local_irq_save(flags);
ret = __pcpu_freelist_pop(s);
local_irq_restore(flags);
return ret;
}
kernel/bpf/percpu_freelist.h
View file @ dcab2483
......@@ -22,8 +22,12 @@ struct pcpu_freelist_node {
struct pcpu_freelist_node *next;
};
/* pcpu_freelist_* do spin_lock_irqsave. */
void pcpu_freelist_push(struct pcpu_freelist *, struct pcpu_freelist_node *);
struct pcpu_freelist_node *pcpu_freelist_pop(struct pcpu_freelist *);
/* __pcpu_freelist_* do spin_lock only. caller must disable irqs. */
void __pcpu_freelist_push(struct pcpu_freelist *, struct pcpu_freelist_node *);
struct pcpu_freelist_node *__pcpu_freelist_pop(struct pcpu_freelist *);
void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
u32 nr_elems);
int pcpu_freelist_init(struct pcpu_freelist *);
......
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