Messages in this thread Patch in this message | | | From | Ravi Bangoria <> | Subject | [RFC 4/4] trace_uprobe: Fix multiple update of same semaphores | Date | Wed, 28 Feb 2018 13:23:45 +0530 |
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For tiny binaries/libraries, different mmap regions points to the same file portion. In such cases, we may increment semaphore multiple times. But while de-registration, semaphore will get decremented only once, leaving semaphore > 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 semaphore 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:
# echo 1 > events/sdt_tick/loop2/enable # ./Workspace/sdt_prog/tick & # dd if=/proc//mem bs=1 count=1 skip=268566582 2>/dev/null | xxd 0000000: 02 .
# echo 0 > events/sdt_tick/loop2/enable # dd if=/proc//mem bs=1 count=1 skip=268566582 2>/dev/null | xxd 0000000: 01 .
After patch:
# echo 1 > events/sdt_tick/loop2/enable # ./Workspace/sdt_prog/tick & # dd if=/proc//mem bs=1 count=1 skip=268566582 2>/dev/null | xxd 0000000: 01 .
# echo 0 > events/sdt_tick/loop2/enable # dd if=/proc//mem bs=1 count=1 skip=268566582 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, 102 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index d14aafc..3f1e8bd 100644 --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -49,6 +49,11 @@ 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 */ @@ -60,6 +65,8 @@ struct trace_uprobe { char *filename; unsigned long offset; unsigned long sdt_offset; /* sdt semaphore offset */ + struct sdt_mm_list *sml; + struct rw_semaphore sml_rw_sem; unsigned long nhit; struct trace_probe tp; }; @@ -273,6 +280,7 @@ 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: @@ -953,6 +961,75 @@ static bool sdt_valid_vma(struct trace_uprobe *tu, struct vm_area_struct *vma) return 0; } +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) { + pr_info("sdt_add_mm_list failed.\n"); + 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; +} + /* * TODO: Adding this defination in include/linux/uprobes.h throws * warnings about address_sapce. Adding it here for the time being. @@ -970,20 +1047,26 @@ static void sdt_increment_sem(struct trace_uprobe *tu) if (IS_ERR(info)) goto out; + down_write(&tu->sml_rw_sem); while (info) { down_write(&info->mm->mmap_sem); vma = sdt_find_vma(info->mm, tu); if (!vma) goto cont; + if (sdt_check_mm_list(tu, info->mm)) + goto cont; + vaddr = offset_to_vaddr(vma, tu->sdt_offset); - sdt_update_sem(info->mm, vaddr, 1); + if (!sdt_update_sem(info->mm, vaddr, 1)) + sdt_add_mm_list(tu, info->mm); cont: up_write(&info->mm->mmap_sem); mmput(info->mm); info = free_uprobe_map_info(info); } + up_write(&tu->sml_rw_sem); out: uprobe_end_dup_mmap(); @@ -1001,8 +1084,16 @@ 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 = offset_to_vaddr(vma, tu->sdt_offset); - sdt_update_sem(vma->vm_mm, vaddr, 1); + if (!sdt_update_sem(vma->vm_mm, vaddr, 1)) + sdt_add_mm_list(tu, vma->vm_mm); + +cont: + up_write(&tu->sml_rw_sem); } mutex_unlock(&uprobe_lock); } @@ -1017,7 +1108,11 @@ static void sdt_decrement_sem(struct trace_uprobe *tu) if (IS_ERR(info)) return; + 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); if (vma) { @@ -1025,10 +1120,14 @@ static void sdt_decrement_sem(struct trace_uprobe *tu) sdt_update_sem(info->mm, vaddr, -1); } up_write(&info->mm->mmap_sem); - + sdt_del_mm_list(tu, info->mm); + +cont: mmput(info->mm); info = free_uprobe_map_info(info); } + sdt_flush_mm_list(tu); + up_write(&tu->sml_rw_sem); } typedef bool (*filter_func_t)(struct uprobe_consumer *self, -- 1.8.3.1
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