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Subject[PATCH 6/8] trace_uprobe/sdt: Fix multiple update of same reference counter
Date
For tiny binaries/libraries, different mmap regions points to the
same file portion. In such cases, we may increment reference counter
multiple times. But while de-registration, reference counter will get
decremented only by once leaving reference counter > 0 even if no one
is tracing on that marker.

Ensure increment and decrement happens in sync by keeping list of
mms in trace_uprobe. Increment reference counter only if mm is not
present in the list and decrement only if mm is present in the list.

Example

# echo "p:sdt_tick/loop2 /tmp/tick:0x6e4(0x10036)" > uprobe_events

Before patch:

# perf stat -a -e sdt_tick:loop2
# /tmp/tick
# dd if=/proc/`pgrep tick`/mem bs=1 count=1 skip=$(( 0x10020036 )) 2>/dev/null | xxd
0000000: 02 .

# pkill perf
# dd if=/proc/`pgrep tick`/mem bs=1 count=1 skip=$(( 0x10020036 )) 2>/dev/null | xxd
0000000: 01 .

After patch:

# perf stat -a -e sdt_tick:loop2
# /tmp/tick
# dd if=/proc/`pgrep tick`/mem bs=1 count=1 skip=$(( 0x10020036 )) 2>/dev/null | xxd
0000000: 01 .

# pkill perf
# dd if=/proc/`pgrep tick`/mem bs=1 count=1 skip=$(( 0x10020036 )) 2>/dev/null | xxd
0000000: 00 .

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
---
kernel/trace/trace_uprobe.c | 105 +++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 103 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index b6c9b48..9bf3f7a 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -50,6 +50,11 @@ struct trace_uprobe_filter {
struct list_head perf_events;
};

+struct sdt_mm_list {
+ struct mm_struct *mm;
+ struct sdt_mm_list *next;
+};
+
/*
* uprobe event core functions
*/
@@ -61,6 +66,8 @@ struct trace_uprobe {
char *filename;
unsigned long offset;
unsigned long ref_ctr_offset;
+ struct sdt_mm_list *sml;
+ struct rw_semaphore sml_rw_sem;
unsigned long nhit;
struct trace_probe tp;
};
@@ -274,6 +281,7 @@ static inline bool is_ret_probe(struct trace_uprobe *tu)
if (is_ret)
tu->consumer.ret_handler = uretprobe_dispatcher;
init_trace_uprobe_filter(&tu->filter);
+ init_rwsem(&tu->sml_rw_sem);
return tu;

error:
@@ -921,6 +929,74 @@ static void uretprobe_trace_func(struct trace_uprobe *tu, unsigned long func,
return trace_handle_return(s);
}

+static bool sdt_check_mm_list(struct trace_uprobe *tu, struct mm_struct *mm)
+{
+ struct sdt_mm_list *tmp = tu->sml;
+
+ if (!tu->sml || !mm)
+ return false;
+
+ while (tmp) {
+ if (tmp->mm == mm)
+ return true;
+ tmp = tmp->next;
+ }
+
+ return false;
+}
+
+static void sdt_add_mm_list(struct trace_uprobe *tu, struct mm_struct *mm)
+{
+ struct sdt_mm_list *tmp;
+
+ tmp = kzalloc(sizeof(*tmp), GFP_KERNEL);
+ if (!tmp)
+ return;
+
+ tmp->mm = mm;
+ tmp->next = tu->sml;
+ tu->sml = tmp;
+}
+
+static void sdt_del_mm_list(struct trace_uprobe *tu, struct mm_struct *mm)
+{
+ struct sdt_mm_list *prev, *curr;
+
+ if (!tu->sml)
+ return;
+
+ if (tu->sml->mm == mm) {
+ curr = tu->sml;
+ tu->sml = tu->sml->next;
+ kfree(curr);
+ return;
+ }
+
+ prev = tu->sml;
+ curr = tu->sml->next;
+ while (curr) {
+ if (curr->mm == mm) {
+ prev->next = curr->next;
+ kfree(curr);
+ return;
+ }
+ prev = curr;
+ curr = curr->next;
+ }
+}
+
+static void sdt_flush_mm_list(struct trace_uprobe *tu)
+{
+ struct sdt_mm_list *next, *curr = tu->sml;
+
+ while (curr) {
+ next = curr->next;
+ kfree(curr);
+ curr = next;
+ }
+ tu->sml = NULL;
+}
+
static bool sdt_valid_vma(struct trace_uprobe *tu, struct vm_area_struct *vma)
{
unsigned long vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
@@ -989,17 +1065,25 @@ static void sdt_increment_ref_ctr(struct trace_uprobe *tu)
if (IS_ERR(info))
goto out;

+ down_write(&tu->sml_rw_sem);
while (info) {
+ if (sdt_check_mm_list(tu, info->mm))
+ goto cont;
+
down_write(&info->mm->mmap_sem);

vma = sdt_find_vma(info->mm, tu);
vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
- sdt_update_ref_ctr(info->mm, vaddr, 1);
+ if (!sdt_update_ref_ctr(info->mm, vaddr, 1))
+ sdt_add_mm_list(tu, info->mm);

up_write(&info->mm->mmap_sem);
+
+cont:
mmput(info->mm);
info = uprobe_free_map_info(info);
}
+ up_write(&tu->sml_rw_sem);

out:
uprobe_end_dup_mmap();
@@ -1020,8 +1104,16 @@ void trace_uprobe_mmap_callback(struct vm_area_struct *vma)
!trace_probe_is_enabled(&tu->tp))
continue;

+ down_write(&tu->sml_rw_sem);
+ if (sdt_check_mm_list(tu, vma->vm_mm))
+ goto cont;
+
vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
- sdt_update_ref_ctr(vma->vm_mm, vaddr, 1);
+ if (!sdt_update_ref_ctr(vma->vm_mm, vaddr, 1))
+ sdt_add_mm_list(tu, vma->vm_mm);
+
+cont:
+ up_write(&tu->sml_rw_sem);
}
mutex_unlock(&uprobe_lock);
}
@@ -1038,7 +1130,11 @@ static void sdt_decrement_ref_ctr(struct trace_uprobe *tu)
if (IS_ERR(info))
goto out;

+ down_write(&tu->sml_rw_sem);
while (info) {
+ if (!sdt_check_mm_list(tu, info->mm))
+ goto cont;
+
down_write(&info->mm->mmap_sem);

vma = sdt_find_vma(info->mm, tu);
@@ -1046,9 +1142,14 @@ static void sdt_decrement_ref_ctr(struct trace_uprobe *tu)
sdt_update_ref_ctr(info->mm, vaddr, -1);

up_write(&info->mm->mmap_sem);
+ sdt_del_mm_list(tu, info->mm);
+
+cont:
mmput(info->mm);
info = uprobe_free_map_info(info);
}
+ sdt_flush_mm_list(tu);
+ up_write(&tu->sml_rw_sem);

out:
uprobe_end_dup_mmap();
--
1.8.3.1
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