netdev - Re: [PATCH bpf-next] bpf: check that BPF programs run with preemption disabled

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Message-ID: <6A67533E-51B3-428A-9236-B98321119446@fb.com>
Date:   Tue, 29 Jan 2019 07:00:40 +0000
From:   Song Liu <songliubraving@...com>
To:     Alexei Starovoitov <ast@...nel.org>
CC:     David Miller <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "paulmck@...ux.ibm.com" <paulmck@...ux.ibm.com>,
        "will.deacon@....com" <will.deacon@....com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next] bpf: check that BPF programs run with preemption
 disabled



> On Jan 28, 2019, at 5:21 PM, Alexei Starovoitov <ast@...nel.org> wrote:
> 
> From: Peter Zijlstra <peterz@...radead.org>
> 
> Introduce cant_sleep() macro for annotation of functions that cannot sleep.
> 
> Use it in BPF_PROG_RUN to catch execution of BPF programs
> in preemptable context.
> 
> Suggested-by: Jann Horn <jannh@...gle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

Acked-by: Song Liu <songliubraving@...com>


> ---
> include/linux/filter.h |  2 +-
> include/linux/kernel.h | 14 ++++++++++++--
> kernel/sched/core.c    | 28 ++++++++++++++++++++++++++++
> 3 files changed, 41 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index e4b473f85b46..7e87863617b3 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -533,7 +533,7 @@ struct sk_filter {
> 	struct bpf_prog	*prog;
> };
> 
> -#define BPF_PROG_RUN(filter, ctx)  (*(filter)->bpf_func)(ctx, (filter)->insnsi)
> +#define BPF_PROG_RUN(filter, ctx)  ({ cant_sleep(); (*(filter)->bpf_func)(ctx, (filter)->insnsi); })
> 
> #define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 8f0e68e250a7..a8868a32098c 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -245,8 +245,10 @@ extern int _cond_resched(void);
> #endif
> 
> #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> -  void ___might_sleep(const char *file, int line, int preempt_offset);
> -  void __might_sleep(const char *file, int line, int preempt_offset);
> +extern void ___might_sleep(const char *file, int line, int preempt_offset);
> +extern void __might_sleep(const char *file, int line, int preempt_offset);
> +extern void __cant_sleep(const char *file, int line, int preempt_offset);
> +
> /**
>  * might_sleep - annotation for functions that can sleep
>  *
> @@ -259,6 +261,13 @@ extern int _cond_resched(void);
>  */
> # define might_sleep() \
> 	do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
> +/**
> + * cant_sleep - annotation for functions that cannot sleep
> + *
> + * this macro will print a stack trace if it is executed with preemption enabled
> + */
> +# define cant_sleep() \
> +	do { __cant_sleep(__FILE__, __LINE__, 0); } while (0)
> # define sched_annotate_sleep()	(current->task_state_change = 0)
> #else
>   static inline void ___might_sleep(const char *file, int line,
> @@ -266,6 +275,7 @@ extern int _cond_resched(void);
>   static inline void __might_sleep(const char *file, int line,
> 				   int preempt_offset) { }
> # define might_sleep() do { might_resched(); } while (0)
> +# define cant_sleep() do { } while (0)
> # define sched_annotate_sleep() do { } while (0)
> #endif
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a674c7db2f29..1dcbff62f973 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6149,6 +6149,34 @@ void ___might_sleep(const char *file, int line, int preempt_offset)
> 	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
> }
> EXPORT_SYMBOL(___might_sleep);
> +
> +void __cant_sleep(const char *file, int line, int preempt_offset)
> +{
> +	static unsigned long prev_jiffy;
> +
> +	if (irqs_disabled())
> +		return;
> +
> +	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
> +		return;
> +
> +	if (preempt_count() > preempt_offset)
> +		return;
> +
> +	if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
> +		return;
> +	prev_jiffy = jiffies;
> +
> +	printk(KERN_ERR "BUG: assuming atomic context at %s:%d\n", file, line);
> +	printk(KERN_ERR "in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n",
> +			in_atomic(), irqs_disabled(),
> +			current->pid, current->comm);
> +
> +	debug_show_held_locks(current);
> +	dump_stack();
> +	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
> +}
> +EXPORT_SYMBOL_GPL(__cant_sleep);
> #endif
> 
> #ifdef CONFIG_MAGIC_SYSRQ
> -- 
> 2.20.0
>