netdev - Re: [PATCH v2 bpf-next] bpf/stackmap: fix deadlock with rq_lock in bpf_get

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Message-ID: <CAADnVQKn3RZnAZAOSg1yoQmo9doeGouEBkcFzmZGWLU7QqjJOA@mail.gmail.com>
Date:   Wed, 16 Oct 2019 10:43:36 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        sashal@...nel.org, Kernel Team <kernel-team@...com>,
        stable <stable@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH v2 bpf-next] bpf/stackmap: fix deadlock with rq_lock in bpf_get_stack()

On Mon, Oct 14, 2019 at 10:12 AM Song Liu <songliubraving@...com> wrote:
>
> 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: commit 615755a77b24 ("bpf: extend stackmap to save binary_build_id+offset instead of address")
> Cc: stable@...r.kernel.org # v4.17+
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Signed-off-by: Song Liu <songliubraving@...com>

I fixed 'Fixes' tag and applied to bpf-next.
Thanks