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SubjectRe: [PATCH 5/8] trace_uprobe: Support SDT markers having reference count (semaphore)
Hi Ravi,

On Tue, 13 Mar 2018 18:26:00 +0530
Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> wrote:

> 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:
>
> <path>:<offset>[(ref_ctr_offset)]

Would you mean
<path>:<offset>(<ref_ctr_offset>)
?

or use "[]" for delimiter?

Since,

> @@ -454,6 +458,26 @@ static int create_trace_uprobe(int argc, char **argv)
> goto fail_address_parse;
> }
>
> + /* Parse reference counter offset if specified. */
> + rctr = strchr(arg, '(');

This seems you choose "()" for delimiter.

> + if (rctr) {
> + rctr_end = strchr(arg, ')');

rctr_end = strchr(rctr, ')');

? since we are sure rctr != NULL.

> + if (rctr > rctr_end || *(rctr_end + 1) != 0) {
> + ret = -EINVAL;
> + pr_info("Invalid reference counter offset.\n");
> + goto fail_address_parse;
> + }


Also

> +
> + *rctr++ = 0;
> + *rctr_end = 0;

Please consider to use '\0' for nul;

Thanks,



> + ret = kstrtoul(rctr, 0, &ref_ctr_offset);
> + if (ret) {
> + pr_info("Invalid reference counter offset.\n");
> + goto fail_address_parse;
> + }
> + }
> +
> + /* Parse uprobe offset. */
> ret = kstrtoul(arg, 0, &offset);
> if (ret)
> goto fail_address_parse;
> @@ -488,6 +512,7 @@ static int create_trace_uprobe(int argc, char **argv)
> goto fail_address_parse;
> }
> tu->offset = offset;
> + tu->ref_ctr_offset = ref_ctr_offset;
> tu->inode = inode;
> tu->filename = kstrdup(filename, GFP_KERNEL);
>
> @@ -620,6 +645,8 @@ static int probes_seq_show(struct seq_file *m, void *v)
> break;
> }
> }
> + if (tu->ref_ctr_offset)
> + seq_printf(m, "(0x%lx)", tu->ref_ctr_offset);
>
> for (i = 0; i < tu->tp.nr_args; i++)
> seq_printf(m, " %s=%s", tu->tp.args[i].name, tu->tp.args[i].comm);
> @@ -894,6 +921,139 @@ static void uretprobe_trace_func(struct trace_uprobe *tu, unsigned long func,
> return trace_handle_return(s);
> }
>
> +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);
> +
> + return tu->ref_ctr_offset &&
> + vma->vm_file &&
> + file_inode(vma->vm_file) == tu->inode &&
> + vma->vm_flags & VM_WRITE &&
> + vma->vm_start <= vaddr &&
> + vma->vm_end > vaddr;
> +}
> +
> +static struct vm_area_struct *
> +sdt_find_vma(struct mm_struct *mm, struct trace_uprobe *tu)
> +{
> + struct vm_area_struct *tmp;
> +
> + for (tmp = mm->mmap; tmp != NULL; tmp = tmp->vm_next)
> + if (sdt_valid_vma(tu, tmp))
> + return tmp;
> +
> + return NULL;
> +}
> +
> +/*
> + * Reference count gate the invocation of probe. If present,
> + * by default reference count is 0. One needs to increment
> + * it before tracing the probe and decrement it when done.
> + */
> +static int
> +sdt_update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d)
> +{
> + void *kaddr;
> + struct page *page;
> + struct vm_area_struct *vma;
> + int ret = 0;
> + unsigned short orig = 0;
> +
> + if (vaddr == 0)
> + return -EINVAL;
> +
> + ret = get_user_pages_remote(NULL, mm, vaddr, 1,
> + FOLL_FORCE | FOLL_WRITE, &page, &vma, NULL);
> + if (ret <= 0)
> + return ret;
> +
> + kaddr = kmap_atomic(page);
> + memcpy(&orig, kaddr + (vaddr & ~PAGE_MASK), sizeof(orig));
> + orig += d;
> + memcpy(kaddr + (vaddr & ~PAGE_MASK), &orig, sizeof(orig));
> + kunmap_atomic(kaddr);
> +
> + put_page(page);
> + return 0;
> +}
> +
> +static void sdt_increment_ref_ctr(struct trace_uprobe *tu)
> +{
> + struct uprobe_map_info *info;
> + struct vm_area_struct *vma;
> + unsigned long vaddr;
> +
> + uprobe_start_dup_mmap();
> + info = uprobe_build_map_info(tu->inode->i_mapping,
> + tu->ref_ctr_offset, false);
> + if (IS_ERR(info))
> + goto out;
> +
> + while (info) {
> + 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);
> +
> + up_write(&info->mm->mmap_sem);
> + mmput(info->mm);
> + info = uprobe_free_map_info(info);
> + }
> +
> +out:
> + uprobe_end_dup_mmap();
> +}
> +
> +/* Called with down_write(&vma->vm_mm->mmap_sem) */
> +void trace_uprobe_mmap_callback(struct vm_area_struct *vma)
> +{
> + struct trace_uprobe *tu;
> + unsigned long vaddr;
> +
> + if (!(vma->vm_flags & VM_WRITE))
> + return;
> +
> + mutex_lock(&uprobe_lock);
> + list_for_each_entry(tu, &uprobe_list, list) {
> + if (!sdt_valid_vma(tu, vma) ||
> + !trace_probe_is_enabled(&tu->tp))
> + continue;
> +
> + vaddr = vma_offset_to_vaddr(vma, tu->ref_ctr_offset);
> + sdt_update_ref_ctr(vma->vm_mm, vaddr, 1);
> + }
> + mutex_unlock(&uprobe_lock);
> +}
> +
> +static void sdt_decrement_ref_ctr(struct trace_uprobe *tu)
> +{
> + struct vm_area_struct *vma;
> + unsigned long vaddr;
> + struct uprobe_map_info *info;
> +
> + uprobe_start_dup_mmap();
> + info = uprobe_build_map_info(tu->inode->i_mapping,
> + tu->ref_ctr_offset, false);
> + if (IS_ERR(info))
> + goto out;
> +
> + while (info) {
> + 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);
> +
> + up_write(&info->mm->mmap_sem);
> + mmput(info->mm);
> + info = uprobe_free_map_info(info);
> + }
> +
> +out:
> + uprobe_end_dup_mmap();
> +}
> +
> typedef bool (*filter_func_t)(struct uprobe_consumer *self,
> enum uprobe_filter_ctx ctx,
> struct mm_struct *mm);
> @@ -939,6 +1099,9 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self,
> if (ret)
> goto err_buffer;
>
> + if (tu->ref_ctr_offset)
> + sdt_increment_ref_ctr(tu);
> +
> return 0;
>
> err_buffer:
> @@ -979,6 +1142,9 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self,
>
> WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>
> + if (tu->ref_ctr_offset)
> + sdt_decrement_ref_ctr(tu);
> +
> uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>
> @@ -1423,6 +1589,8 @@ static __init int init_uprobe_trace(void)
> /* Profile interface */
> trace_create_file("uprobe_profile", 0444, d_tracer,
> NULL, &uprobe_profile_ops);
> +
> + uprobe_mmap_callback = trace_uprobe_mmap_callback;
> return 0;
> }
>
> --
> 1.8.3.1
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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