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Date: Fri, 17 Apr 2020 16:38:10 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...e.hu>
Cc: Jiri Olsa <jolsa@...nel.org>,
"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
"David S. Miller" <davem@...emloft.net>,
Peter Zijlstra <peterz@...radead.org>,
lkml <linux-kernel@...r.kernel.org>,
"bibo,mao" <bibo.mao@...el.com>,
"Ziqian SUN (Zamir)" <zsun@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCHv2] kretprobe: Prevent triggering kretprobe from within
kprobe_flush_task
On Thu, 16 Apr 2020 16:31:04 +0200
Jiri Olsa <jolsa@...hat.com> wrote:
> Ziqian reported lockup when adding retprobe on _raw_spin_lock_irqsave.
> My test was also able to trigger lockdep output:
>
> ============================================
> WARNING: possible recursive locking detected
> 5.6.0-rc6+ #6 Not tainted
> --------------------------------------------
> sched-messaging/2767 is trying to acquire lock:
> ffffffff9a492798 (&(kretprobe_table_locks[i].lock)){-.-.}, at: kretprobe_hash_lock+0x52/0xa0
>
> but task is already holding lock:
> ffffffff9a491a18 (&(kretprobe_table_locks[i].lock)){-.-.}, at: kretprobe_trampoline+0x0/0x50
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(&(kretprobe_table_locks[i].lock));
> lock(&(kretprobe_table_locks[i].lock));
>
> *** DEADLOCK ***
>
> May be due to missing lock nesting notation
>
> 1 lock held by sched-messaging/2767:
> #0: ffffffff9a491a18 (&(kretprobe_table_locks[i].lock)){-.-.}, at: kretprobe_trampoline+0x0/0x50
>
> stack backtrace:
> CPU: 3 PID: 2767 Comm: sched-messaging Not tainted 5.6.0-rc6+ #6
> Call Trace:
> dump_stack+0x96/0xe0
> __lock_acquire.cold.57+0x173/0x2b7
> ? native_queued_spin_lock_slowpath+0x42b/0x9e0
> ? lockdep_hardirqs_on+0x590/0x590
> ? __lock_acquire+0xf63/0x4030
> lock_acquire+0x15a/0x3d0
> ? kretprobe_hash_lock+0x52/0xa0
> _raw_spin_lock_irqsave+0x36/0x70
> ? kretprobe_hash_lock+0x52/0xa0
> kretprobe_hash_lock+0x52/0xa0
> trampoline_handler+0xf8/0x940
> ? kprobe_fault_handler+0x380/0x380
> ? find_held_lock+0x3a/0x1c0
> kretprobe_trampoline+0x25/0x50
> ? lock_acquired+0x392/0xbc0
> ? _raw_spin_lock_irqsave+0x50/0x70
> ? __get_valid_kprobe+0x1f0/0x1f0
> ? _raw_spin_unlock_irqrestore+0x3b/0x40
> ? finish_task_switch+0x4b9/0x6d0
> ? __switch_to_asm+0x34/0x70
> ? __switch_to_asm+0x40/0x70
>
> The code within the kretprobe handler checks for probe reentrancy,
> so we won't trigger any _raw_spin_lock_irqsave probe in there.
>
> The problem is in outside kprobe_flush_task, where we call:
>
> kprobe_flush_task
> kretprobe_table_lock
> raw_spin_lock_irqsave
> _raw_spin_lock_irqsave
>
> where _raw_spin_lock_irqsave triggers the kretprobe and installs
> kretprobe_trampoline handler on _raw_spin_lock_irqsave return.
>
> The kretprobe_trampoline handler is then executed with already
> locked kretprobe_table_locks, and first thing it does is to
> lock kretprobe_table_locks ;-) the whole lockup path like:
>
> kprobe_flush_task
> kretprobe_table_lock
> raw_spin_lock_irqsave
> _raw_spin_lock_irqsave ---> probe triggered, kretprobe_trampoline installed
>
> ---> kretprobe_table_locks locked
>
> kretprobe_trampoline
> trampoline_handler
> kretprobe_hash_lock(current, &head, &flags); <--- deadlock
>
> Adding kprobe_busy_begin/end helpers that mark code with fake
> probe installed to prevent triggering of another kprobe within
> this code.
>
> Using these helpers in kprobe_flush_task, so the probe recursion
> protection check is hit and the probe is never set to prevent
> above lockup.
>
Thanks Jiri!
Ingo, could you pick this up?
Regards,
> Fixes: ef53d9c5e4da ('kprobes: improve kretprobe scalability with hashed locking')
> Cc: stable@...r.kernel.org
> Reported-by: "Ziqian SUN (Zamir)" <zsun@...hat.com>
> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
> arch/x86/kernel/kprobes/core.c | 16 +++-------------
> include/linux/kprobes.h | 4 ++++
> kernel/kprobes.c | 24 ++++++++++++++++++++++++
> 3 files changed, 31 insertions(+), 13 deletions(-)
>
> v2 changes: updated changelog with Fixes/Ack and Cc stable
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 4d7022a740ab..a12adbe1559d 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -753,16 +753,11 @@ asm(
> NOKPROBE_SYMBOL(kretprobe_trampoline);
> STACK_FRAME_NON_STANDARD(kretprobe_trampoline);
>
> -static struct kprobe kretprobe_kprobe = {
> - .addr = (void *)kretprobe_trampoline,
> -};
> -
> /*
> * Called from kretprobe_trampoline
> */
> __used __visible void *trampoline_handler(struct pt_regs *regs)
> {
> - struct kprobe_ctlblk *kcb;
> struct kretprobe_instance *ri = NULL;
> struct hlist_head *head, empty_rp;
> struct hlist_node *tmp;
> @@ -772,16 +767,12 @@ __used __visible void *trampoline_handler(struct pt_regs *regs)
> void *frame_pointer;
> bool skipped = false;
>
> - preempt_disable();
> -
> /*
> * Set a dummy kprobe for avoiding kretprobe recursion.
> * Since kretprobe never run in kprobe handler, kprobe must not
> * be running at this point.
> */
> - kcb = get_kprobe_ctlblk();
> - __this_cpu_write(current_kprobe, &kretprobe_kprobe);
> - kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> + kprobe_busy_begin();
>
> INIT_HLIST_HEAD(&empty_rp);
> kretprobe_hash_lock(current, &head, &flags);
> @@ -857,7 +848,7 @@ __used __visible void *trampoline_handler(struct pt_regs *regs)
> __this_cpu_write(current_kprobe, &ri->rp->kp);
> ri->ret_addr = correct_ret_addr;
> ri->rp->handler(ri, regs);
> - __this_cpu_write(current_kprobe, &kretprobe_kprobe);
> + __this_cpu_write(current_kprobe, &kprobe_busy);
> }
>
> recycle_rp_inst(ri, &empty_rp);
> @@ -873,8 +864,7 @@ __used __visible void *trampoline_handler(struct pt_regs *regs)
>
> kretprobe_hash_unlock(current, &flags);
>
> - __this_cpu_write(current_kprobe, NULL);
> - preempt_enable();
> + kprobe_busy_end();
>
> hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
> hlist_del(&ri->hlist);
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 04bdaf01112c..645fd401c856 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -350,6 +350,10 @@ static inline struct kprobe_ctlblk *get_kprobe_ctlblk(void)
> return this_cpu_ptr(&kprobe_ctlblk);
> }
>
> +extern struct kprobe kprobe_busy;
> +void kprobe_busy_begin(void);
> +void kprobe_busy_end(void);
> +
> kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset);
> int register_kprobe(struct kprobe *p);
> void unregister_kprobe(struct kprobe *p);
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 2625c241ac00..75bb4a8458e7 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1236,6 +1236,26 @@ __releases(hlist_lock)
> }
> NOKPROBE_SYMBOL(kretprobe_table_unlock);
>
> +struct kprobe kprobe_busy = {
> + .addr = (void *) get_kprobe,
> +};
> +
> +void kprobe_busy_begin(void)
> +{
> + struct kprobe_ctlblk *kcb;
> +
> + preempt_disable();
> + __this_cpu_write(current_kprobe, &kprobe_busy);
> + kcb = get_kprobe_ctlblk();
> + kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> +}
> +
> +void kprobe_busy_end(void)
> +{
> + __this_cpu_write(current_kprobe, NULL);
> + preempt_enable();
> +}
> +
> /*
> * This function is called from finish_task_switch when task tk becomes dead,
> * so that we can recycle any function-return probe instances associated
> @@ -1253,6 +1273,8 @@ void kprobe_flush_task(struct task_struct *tk)
> /* Early boot. kretprobe_table_locks not yet initialized. */
> return;
>
> + kprobe_busy_begin();
> +
> INIT_HLIST_HEAD(&empty_rp);
> hash = hash_ptr(tk, KPROBE_HASH_BITS);
> head = &kretprobe_inst_table[hash];
> @@ -1266,6 +1288,8 @@ void kprobe_flush_task(struct task_struct *tk)
> hlist_del(&ri->hlist);
> kfree(ri);
> }
> +
> + kprobe_busy_end();
> }
> NOKPROBE_SYMBOL(kprobe_flush_task);
>
> --
> 2.18.2
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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