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Date: Wed, 21 Sep 2022 18:17:21 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Waiman Long <longman@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] tracing: Use proper do_arch_spin_lock() API
On Wed, 21 Sep 2022 09:21:52 -0400
Waiman Long <longman@...hat.com> wrote:
> It was found that some tracing functions acquire a arch_spinlock_t with
> preemption and irqs enabled. That can be problematic in case preemption
> happens after acquiring the lock. Use the proper do_arch_spin_lock()
> API with preemption disabled to make sure that this won't happen unless
> it is obvious that either preemption or irqs has been disabled .
>
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
> kernel/trace/trace.c | 52 ++++++++++++++++++++------------------------
> 1 file changed, 24 insertions(+), 28 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index d3005279165d..cbb8520842ad 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1193,12 +1193,12 @@ void *tracing_cond_snapshot_data(struct trace_array *tr)
> {
> void *cond_data = NULL;
>
> - arch_spin_lock(&tr->max_lock);
> + do_arch_spin_lock(&tr->max_lock);
This should actually disable interrupts and not preemption.
>
> if (tr->cond_snapshot)
> cond_data = tr->cond_snapshot->cond_data;
>
> - arch_spin_unlock(&tr->max_lock);
> + do_arch_spin_unlock(&tr->max_lock);
>
> return cond_data;
> }
> @@ -1334,9 +1334,9 @@ int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data,
> goto fail_unlock;
> }
>
> - arch_spin_lock(&tr->max_lock);
> + do_arch_spin_lock(&tr->max_lock);
Same here.
> tr->cond_snapshot = cond_snapshot;
> - arch_spin_unlock(&tr->max_lock);
> + do_arch_spin_unlock(&tr->max_lock);
>
> mutex_unlock(&trace_types_lock);
>
> @@ -1363,7 +1363,7 @@ int tracing_snapshot_cond_disable(struct trace_array *tr)
> {
> int ret = 0;
>
> - arch_spin_lock(&tr->max_lock);
> + do_arch_spin_lock(&tr->max_lock);
And here.
>
> if (!tr->cond_snapshot)
> ret = -EINVAL;
> @@ -1372,7 +1372,7 @@ int tracing_snapshot_cond_disable(struct trace_array *tr)
> tr->cond_snapshot = NULL;
> }
>
> - arch_spin_unlock(&tr->max_lock);
> + do_arch_spin_unlock(&tr->max_lock);
>
> return ret;
> }
> @@ -1819,7 +1819,7 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu,
> return;
> }
>
> - arch_spin_lock(&tr->max_lock);
> + do_arch_spin_lock(&tr->max_lock);
Nothing here is needed, as interrupts had better be disabled when this
function is called. And there's already a:
WARN_ON_ONCE(!irqs_disabled());
>
> /* Inherit the recordable setting from array_buffer */
> if (ring_buffer_record_is_set_on(tr->array_buffer.buffer))
> @@ -1836,7 +1836,7 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu,
> __update_max_tr(tr, tsk, cpu);
>
> out_unlock:
> - arch_spin_unlock(&tr->max_lock);
> + do_arch_spin_unlock(&tr->max_lock);
Nothing needs to be done here.
> }
>
> /**
> @@ -1862,7 +1862,7 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
> return;
> }
>
> - arch_spin_lock(&tr->max_lock);
> + do_arch_spin_lock(&tr->max_lock);
Same here. Interrupts had better be disabled in this function.
>
> ret = ring_buffer_swap_cpu(tr->max_buffer.buffer, tr->array_buffer.buffer, cpu);
>
> @@ -1880,7 +1880,7 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
> WARN_ON_ONCE(ret && ret != -EAGAIN && ret != -EBUSY);
>
> __update_max_tr(tr, tsk, cpu);
> - arch_spin_unlock(&tr->max_lock);
> + do_arch_spin_unlock(&tr->max_lock);
Nothing to do here.
> }
> #endif /* CONFIG_TRACER_MAX_TRACE */
>
> @@ -2413,7 +2413,7 @@ static int trace_save_cmdline(struct task_struct *tsk)
> * nor do we want to disable interrupts,
> * so if we miss here, then better luck next time.
> */
> - if (!arch_spin_trylock(&trace_cmdline_lock))
> + if (!do_arch_spin_trylock(&trace_cmdline_lock))
This is called within the scheduler and wake up, so interrupts had better
be disabled (run queue lock is held).
> return 0;
>
> idx = savedcmd->map_pid_to_cmdline[tpid];
> @@ -2427,7 +2427,7 @@ static int trace_save_cmdline(struct task_struct *tsk)
> savedcmd->map_cmdline_to_pid[idx] = tsk->pid;
> set_cmdline(idx, tsk->comm);
>
> - arch_spin_unlock(&trace_cmdline_lock);
> + do_arch_spin_unlock(&trace_cmdline_lock);
Nothing to do here.
>
> return 1;
> }
> @@ -2461,13 +2461,11 @@ static void __trace_find_cmdline(int pid, char comm[])
>
> void trace_find_cmdline(int pid, char comm[])
> {
> - preempt_disable();
> - arch_spin_lock(&trace_cmdline_lock);
> + do_arch_spin_lock(&trace_cmdline_lock);
Keep this as is (with the open coded preempt_disable()).
>
> __trace_find_cmdline(pid, comm);
>
> - arch_spin_unlock(&trace_cmdline_lock);
> - preempt_enable();
> + do_arch_spin_unlock(&trace_cmdline_lock);
> }
>
> static int *trace_find_tgid_ptr(int pid)
> @@ -5829,8 +5827,7 @@ static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
> void *v;
> loff_t l = 0;
>
> - preempt_disable();
> - arch_spin_lock(&trace_cmdline_lock);
> + do_arch_spin_lock(&trace_cmdline_lock);
This too.
>
> v = &savedcmd->map_cmdline_to_pid[0];
> while (l <= *pos) {
> @@ -5844,8 +5841,7 @@ static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
>
> static void saved_cmdlines_stop(struct seq_file *m, void *v)
> {
> - arch_spin_unlock(&trace_cmdline_lock);
> - preempt_enable();
> + do_arch_spin_unlock(&trace_cmdline_lock);
And this.
> }
>
> static int saved_cmdlines_show(struct seq_file *m, void *v)
> @@ -5890,9 +5886,9 @@ tracing_saved_cmdlines_size_read(struct file *filp, char __user *ubuf,
> char buf[64];
> int r;
>
> - arch_spin_lock(&trace_cmdline_lock);
> + do_arch_spin_lock(&trace_cmdline_lock);
Yeah, we should add preempt_disable() here.
> r = scnprintf(buf, sizeof(buf), "%u\n", savedcmd->cmdline_num);
> - arch_spin_unlock(&trace_cmdline_lock);
> + do_arch_spin_unlock(&trace_cmdline_lock);
>
> return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
> }
> @@ -5917,10 +5913,10 @@ static int tracing_resize_saved_cmdlines(unsigned int val)
> return -ENOMEM;
> }
>
> - arch_spin_lock(&trace_cmdline_lock);
> + do_arch_spin_lock(&trace_cmdline_lock);
And here.
> savedcmd_temp = savedcmd;
> savedcmd = s;
> - arch_spin_unlock(&trace_cmdline_lock);
> + do_arch_spin_unlock(&trace_cmdline_lock);
> free_saved_cmdlines_buffer(savedcmd_temp);
>
> return 0;
> @@ -6373,10 +6369,10 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
>
> #ifdef CONFIG_TRACER_SNAPSHOT
> if (t->use_max_tr) {
> - arch_spin_lock(&tr->max_lock);
> + do_arch_spin_lock(&tr->max_lock);
Add preemption disabling.
> if (tr->cond_snapshot)
> ret = -EBUSY;
> - arch_spin_unlock(&tr->max_lock);
> + do_arch_spin_unlock(&tr->max_lock);
> if (ret)
> goto out;
> }
> @@ -7436,10 +7432,10 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
> goto out;
> }
>
> - arch_spin_lock(&tr->max_lock);
> + do_arch_spin_lock(&tr->max_lock);
And this should disable interrupts first.
-- Steve
> if (tr->cond_snapshot)
> ret = -EBUSY;
> - arch_spin_unlock(&tr->max_lock);
> + do_arch_spin_unlock(&tr->max_lock);
> if (ret)
> goto out;
>
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