Messages in this thread | | | Date | Wed, 21 Sep 2022 20:50:27 -0400 | Subject | Re: [PATCH 2/2] tracing: Use proper do_arch_spin_lock() API | From | Waiman Long <> |
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On 9/21/22 18:17, Steven Rostedt wrote: > On Wed, 21 Sep 2022 09:21:52 -0400 > Waiman Long <longman@redhat.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@redhat.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());
Sorry, I missed that.
> >> >> /* 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. Right. > >> } >> >> /** >> @@ -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()). OK. > >> >> __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
Thanks for the comments, will modify the patch as suggested.
Cheers, Longman
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