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Subject[RFC PATCH] trace: prevent preemption in perf_ftrace_function_call()
Date
With CONFIG_DEBUG_PREEMPT we observed reports like:

BUG: using smp_processor_id() in preemptible
caller is perf_ftrace_function_call+0x6f/0x2e0
CPU: 1 PID: 680 Comm: a.out Not tainted
Call Trace:
<TASK>
dump_stack_lvl+0x8d/0xcf
check_preemption_disabled+0x104/0x110
? optimize_nops.isra.7+0x230/0x230
? text_poke_bp_batch+0x9f/0x310
perf_ftrace_function_call+0x6f/0x2e0
...
__text_poke+0x5/0x620
text_poke_bp_batch+0x9f/0x310

This tell us the CPU could be changed after task is preempted, and
the checking on CPU before preemption is helpless.

This patch just turn off preemption in perf_ftrace_function_call()
to prevent CPU changing.

Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com>
---
kernel/trace/trace_event_perf.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 6aed10e..5486b18 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -438,15 +438,17 @@ void perf_trace_buf_update(void *record, u16 type)
int rctx;
int bit;

+ preempt_disable_notrace();
+
if (!rcu_is_watching())
- return;
+ goto out;

if ((unsigned long)ops->private != smp_processor_id())
- return;
+ goto out;

bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
- return;
+ goto out;

event = container_of(ops, struct perf_event, ftrace_ops);

@@ -468,16 +470,18 @@ void perf_trace_buf_update(void *record, u16 type)

entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx);
if (!entry)
- goto out;
+ goto out_unlock;

entry->ip = ip;
entry->parent_ip = parent_ip;
perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN,
1, &regs, &head, NULL);

-out:
+out_unlock:
ftrace_test_recursion_unlock(bit);
#undef ENTRY_SIZE
+out:
+ preempt_enable_notrace();
}

static int perf_ftrace_function_register(struct perf_event *event)
--
1.8.3.1
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