Userspace Statically Defined Tracepoints[1] are dtrace style markers
inside userspace applications. These markers are added by developer at
important places in the code. Each marker source expands to a single
nop instruction in the compiled code but there may be additional
overhead for computing the marker arguments which expands to couple of
instructions. In case the overhead is more, execution of it can be
ommited by runtime if() condition when no one is tracing on the marker:
if (reference_counter > 0) {
Execute marker instructions;
}
Default value of reference counter is 0. Tracer has to increment the
reference counter before tracing on a marker and decrement it when
done with the tracing.
Implement the reference counter logic in trace_uprobe, leaving core
uprobe infrastructure as is, except one new callback from uprobe_mmap()
to trace_uprobe.
trace_uprobe definition with reference counter will now be:
:[(ref_ctr_offset)]
There are two different cases while enabling the marker,
1. Trace existing process. In this case, find all suitable processes
and increment the reference counter in them.
2. Enable trace before running target binary. In this case, all mmaps
will get notified to trace_uprobe and trace_uprobe will increment
the reference counter if corresponding uprobe is enabled.
At the time of disabling probes, decrement reference counter in all
existing target processes.
[1] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
Note: 'reference counter' is called as 'semaphore' in original Dtrace
(or Systemtap, bcc and even in ELF) documentation and code. But the
term 'semaphore' is misleading in this context. This is just a counter
used to hold number of tracers tracing on a marker. This is not really
used for any synchronization. So we are referring it as 'reference
counter' in kernel / perf code.
Signed-off-by: Ravi Bangoria
Signed-off-by: Fengguang Wu
[Fengguang reported/fixed build failure in RFC patch]
---
include/linux/uprobes.h | 10 +++
kernel/events/uprobes.c | 16 +
kernel/trace/trace_uprobe.c | 162 +++-
3 files changed, 186 insertions(+), 2 deletions(-)
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 7bd2760..2db3ed1 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -122,6 +122,8 @@ struct uprobe_map_info {
unsigned long vaddr;
};
+extern void (*uprobe_mmap_callback)(struct vm_area_struct *vma);
+
extern int set_swbp(struct arch_uprobe *aup, struct mm_struct *mm, unsigned
long vaddr);
extern int set_orig_insn(struct arch_uprobe *aup, struct mm_struct *mm,
unsigned long vaddr);
extern bool is_swbp_insn(uprobe_opcode_t *insn);
@@ -136,6 +138,8 @@ struct uprobe_map_info {
extern void uprobe_munmap(struct vm_area_struct *vma, unsigned long start,
unsigned long end);
extern void uprobe_start_dup_mmap(void);
extern void uprobe_end_dup_mmap(void);
+extern void uprobe_down_write_dup_mmap(void);
+extern void uprobe_up_write_dup_mmap(void);
extern void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm);
extern void uprobe_free_utask(struct task_struct *t);
extern void uprobe_copy_process(struct task_struct *t, unsigned long flags);
@@ -192,6 +196,12 @@ static inline void uprobe_start_dup_mmap(void)
static inline void uprobe_end_dup_mmap(void)
{
}
+static inline void uprobe_down_write_dup_mmap(void)
+{
+}
+static inline void uprobe_up_write_dup_mmap(void)
+{
+}
static inline void
uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
{
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 096d1e6..c691334 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1044,6 +1044,9 @@ static void build_probe_list(struct inode *inode,
spin_unlock(_treelock);
}
+/* Rightnow the only user of this is trace_uprobe. */
+void (*uprobe_mmap_callback)(struct vm_area_struct *vma);
+
/*
* Called from mmap_region/vma_adjust with mm->mmap_sem acquired.
*
@@ -1056,6 +1059,9 @@ int uprobe_mmap(struct vm_area_struct *vma)
struct uprobe *uprobe, *u;
struct inode *inode;
+ if (uprobe_mmap_callback)
+ uprobe_mmap_callback(vma);
+
if (no_uprobe_events() || !valid_vma(vma, true))
return 0;
@@ -1247,6 +1253,16 @@ void uprobe_end_dup_mmap(void)
percpu_up_read(_mmap_sem);
}
+void uprobe_down_write_dup_mmap(void)
+{
+ percpu_down_write(_mmap_sem);
+}
+
+void uprobe_up_write_dup_mmap(void)
+{
+ percpu_up_write(_mmap_sem);
+}
+
void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
{
if (test_bit(MMF_HAS_UPROBES, >flags)) {
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 2014f43..5582c2d 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -25,6 +25,8 @@
