From: Philippe Elie <[email protected]>
Instruction pointer returned by profile_pc() can be a random value. This
break the assumption than we can safely set struct op_sample.eip field to
a magic value to signal to the per-cpu buffer reader side special event
like task switch ending up in a segfault in get_task_mm() when profile_pc()
return ~0UL. Fixed by exchanging the meaning of eip/event field for these
specials events.
Special thanks to Sami Farin who reported the oops and helped patiently
to narrow down the problem.
CC: Andrew Morton <[email protected]>
CC: Linus Torvalds <[email protected]>
CC: Sami Farin <[email protected]>
---
drivers/oprofile/buffer_sync.c | 12 ++++++------
drivers/oprofile/cpu_buffer.c | 2 +-
2 files changed, 7 insertions(+), 7 deletions(-)
Beside Sami, Jesse Barnes already reported this bug two years ago
but I've been unable to understand it at this time.
diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c
index 8134c7e..7a4ccc7 100644
--- a/drivers/oprofile/buffer_sync.c
+++ b/drivers/oprofile/buffer_sync.c
@@ -514,21 +514,21 @@ void sync_buffer(int cpu)
for (i = 0; i < available; ++i) {
struct op_sample * s = &cpu_buf->buffer[cpu_buf->tail_pos];
- if (is_code(s->eip)) {
- if (s->event <= CPU_IS_KERNEL) {
+ if (is_code(s->event)) {
+ if (s->eip <= CPU_IS_KERNEL) {
/* kernel/userspace switch */
- in_kernel = s->event;
+ in_kernel = s->eip;
if (state == sb_buffer_start)
state = sb_sample_start;
- add_kernel_ctx_switch(s->event);
- } else if (s->event == CPU_TRACE_BEGIN) {
+ add_kernel_ctx_switch(s->eip);
+ } else if (s->eip == CPU_TRACE_BEGIN) {
state = sb_bt_start;
add_trace_begin();
} else {
struct mm_struct * oldmm = mm;
/* userspace context switch */
- new = (struct task_struct *)s->event;
+ new = (struct task_struct *)s->eip;
release_mm(oldmm);
mm = take_tasks_mm(new);
diff --git a/drivers/oprofile/cpu_buffer.c b/drivers/oprofile/cpu_buffer.c
index a83c3db..c856530 100644
--- a/drivers/oprofile/cpu_buffer.c
+++ b/drivers/oprofile/cpu_buffer.c
@@ -156,7 +156,7 @@ add_sample(struct oprofile_cpu_buffer * cpu_buf,
static inline void
add_code(struct oprofile_cpu_buffer * buffer, unsigned long value)
{
- add_sample(buffer, ESCAPE_CODE, value);
+ add_sample(buffer, value, ESCAPE_CODE);
}
/* This must be safe from any context. It's safe writing here
-
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