From: Song Liu songliubraving@fb.com
[ Upstream commit eac9153f2b584c702cea02c1f1a57d85aa9aea42 ]
bpf stackmap with build-id lookup (BPF_F_STACK_BUILD_ID) can trigger A-A deadlock on rq_lock():
rcu: INFO: rcu_sched detected stalls on CPUs/tasks: [...] Call Trace: try_to_wake_up+0x1ad/0x590 wake_up_q+0x54/0x80 rwsem_wake+0x8a/0xb0 bpf_get_stack+0x13c/0x150 bpf_prog_fbdaf42eded9fe46_on_event+0x5e3/0x1000 bpf_overflow_handler+0x60/0x100 __perf_event_overflow+0x4f/0xf0 perf_swevent_overflow+0x99/0xc0 ___perf_sw_event+0xe7/0x120 __schedule+0x47d/0x620 schedule+0x29/0x90 futex_wait_queue_me+0xb9/0x110 futex_wait+0x139/0x230 do_futex+0x2ac/0xa50 __x64_sys_futex+0x13c/0x180 do_syscall_64+0x42/0x100 entry_SYSCALL_64_after_hwframe+0x44/0xa9
This can be reproduced by: 1. Start a multi-thread program that does parallel mmap() and malloc(); 2. taskset the program to 2 CPUs; 3. Attach bpf program to trace_sched_switch and gather stackmap with build-id, e.g. with trace.py from bcc tools: trace.py -U -p <pid> -s <some-bin,some-lib> t:sched:sched_switch
A sample reproducer is attached at the end.
This could also trigger deadlock with other locks that are nested with rq_lock.
Fix this by checking whether irqs are disabled. Since rq_lock and all other nested locks are irq safe, it is safe to do up_read() when irqs are not disable. If the irqs are disabled, postpone up_read() in irq_work.
Fixes: 615755a77b24 ("bpf: extend stackmap to save binary_build_id+offset instead of address") Signed-off-by: Song Liu songliubraving@fb.com Signed-off-by: Alexei Starovoitov ast@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Alexei Starovoitov ast@kernel.org Cc: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20191014171223.357174-1-songliubraving@fb.com
Reproducer: ============================ 8< ============================
char *filename;
void *worker(void *p) { void *ptr; int fd; char *pptr;
fd = open(filename, O_RDONLY); if (fd < 0) return NULL; while (1) { struct timespec ts = {0, 1000 + rand() % 2000};
ptr = mmap(NULL, 4096 * 64, PROT_READ, MAP_PRIVATE, fd, 0); usleep(1); if (ptr == MAP_FAILED) { printf("failed to mmap\n"); break; } munmap(ptr, 4096 * 64); usleep(1); pptr = malloc(1); usleep(1); pptr[0] = 1; usleep(1); free(pptr); usleep(1); nanosleep(&ts, NULL); } close(fd); return NULL; }
int main(int argc, char *argv[]) { void *ptr; int i; pthread_t threads[THREAD_COUNT];
if (argc < 2) return 0;
filename = argv[1];
for (i = 0; i < THREAD_COUNT; i++) { if (pthread_create(threads + i, NULL, worker, NULL)) { fprintf(stderr, "Error creating thread\n"); return 0; } }
for (i = 0; i < THREAD_COUNT; i++) pthread_join(threads[i], NULL); return 0; } ============================ 8< ============================
Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/stackmap.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 7cb7a7f98a37..55fff5e6d983 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -292,7 +292,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, bool irq_work_busy = false; struct stack_map_irq_work *work = NULL;
- if (in_nmi()) { + if (irqs_disabled()) { work = this_cpu_ptr(&up_read_work); if (work->irq_work.flags & IRQ_WORK_BUSY) /* cannot queue more up_read, fallback */ @@ -300,8 +300,9 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, }
/* - * We cannot do up_read() in nmi context. To do build_id lookup - * in nmi context, we need to run up_read() in irq_work. We use + * We cannot do up_read() when the irq is disabled, because of + * risk to deadlock with rq_lock. To do build_id lookup when the + * irqs are disabled, we need to run up_read() in irq_work. We use * a percpu variable to do the irq_work. If the irq_work is * already used by another lookup, we fall back to report ips. *