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    SubjectRe: [PATCH 6/8] trace_uprobe/sdt: Fix multiple update of same reference counter
    On Tue, 13 Mar 2018 18:26:01 +0530
    Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> wrote:

    > 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;
    > +};

    Oh, please use struct list_head instead of defining your own pointer-chain :(

    > +
    > /*
    > * 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;

    BTW, is there any reason to use rw_semaphore? (mutex doesn't fit?)

    Thank you,

    > 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
    >


    --
    Masami Hiramatsu <mhiramat@kernel.org>

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