Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore)

Steven Rostedt
2018-08-11T15:38:03Z

On Sat, 11 Aug 2018 00:57:12 -0700
Song Liu <liu.song.a23@gmail.com> wrote:

> > +
> > +static void delayed_uprobe_delete(struct delayed_uprobe *du)
> > +{
> > + if (!du)
> > + return;
> Do we really need this check?

I'd suggest we keep it. It's not a fast path, and operations like this
should really check for NULL.

>
> > + list_del(&du->list);
> > + kfree(du);
> > +}
> > +
> > +static void delayed_uprobe_remove(struct uprobe *uprobe, struct mm_struct *mm)
> > +{
> > + struct list_head *pos, *q;
> > + struct delayed_uprobe *du;
> > +
> > + if (!uprobe && !mm)
> > + return;
> And do we really need this check?

Same here, as it's not a fast path, and it prevents kernel oops if a
NULL is passed in.

>
> > +
> > + list_for_each_safe(pos, q, &delayed_uprobe_list) {
> > + du = list_entry(pos, struct delayed_uprobe, list);
> > +
> > + if (uprobe && mm && du->uprobe == uprobe && du->mm == mm)
> > + delayed_uprobe_delete(du);
> > + else if (!uprobe && du->mm == mm)
> > + delayed_uprobe_delete(du);
> > + else if (!mm && du->uprobe == uprobe)
> > + delayed_uprobe_delete(du);
> > + }
> > +}
> > +
> > +static bool valid_ref_ctr_vma(struct uprobe *uprobe,
> > + struct vm_area_struct *vma)
> > +{
> > + unsigned long vaddr = offset_to_vaddr(vma, uprobe->ref_ctr_offset);
> > +
> > + return uprobe->ref_ctr_offset &&
> > + vma->vm_file &&
> > + file_inode(vma->vm_file) == uprobe->inode &&
> > + (vma->vm_flags & (VM_WRITE|VM_SHARED)) == VM_WRITE &&
> > + vma->vm_start <= vaddr &&
> > + vma->vm_end > vaddr;
> > +}
> > +
> > +static struct vm_area_struct *
> > +find_ref_ctr_vma(struct uprobe *uprobe, struct mm_struct *mm)
> > +{
> > + struct vm_area_struct *tmp;
> > +
> > + for (tmp = mm->mmap; tmp; tmp = tmp->vm_next)
> > + if (valid_ref_ctr_vma(uprobe, tmp))
> > + return tmp;
> > +
> > + return NULL;
> > +}
> > +
> > +static int
> > +__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;
> It is not necessary to initialize ret here.

Agreed.

>
> > + short *ptr;
> > +
> > + if (vaddr == 0 || d == 0)
> > + return -EINVAL;
> > +
> > + ret = get_user_pages_remote(NULL, mm, vaddr, 1,
> > + FOLL_WRITE, &page, &vma, NULL);
> > + if (unlikely(ret <= 0)) {
> > + /*
> > + * We are asking for 1 page. If get_user_pages_remote() fails,
> > + * it may return 0, in that case we have to return error.
> > + */
> > + ret = (ret == 0) ? -EBUSY : ret;
> > + pr_warn("Failed to %s ref_ctr. (%d)\n",
> > + d > 0 ? "increment" : "decrement", ret);
> This warning is not really useful. Seems this function has little information
> about which uprobe is failing here. Maybe we only need warning in the caller
> (or caller of caller).

I'm fine with or without this.

>
> > + return ret;
> > + }
> > +
> > + kaddr = kmap_atomic(page);
> > + ptr = kaddr + (vaddr & ~PAGE_MASK);
> > +
> > + if (unlikely(*ptr + d < 0)) {
> > + pr_warn("ref_ctr going negative. vaddr: 0x%lx, "
> > + "curr val: %d, delta: %d\n", vaddr, *ptr, d);
> > + ret = -EINVAL;
> > + goto out;
> > + }
> > +
> > + *ptr += d;
> > + ret = 0;
> > +out:
> > + kunmap_atomic(kaddr);
> > + put_page(page);
> > + return ret;
> > +}
> > +
> > +static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
> > + bool is_register)
> What's the reason of bool is_register here vs. short d in __update_ref_ctr()?
> Can we use short for both?

bool has more control, but I agree that this function is a bit
confusing.

-- Steve

>
> > +{
> > + struct vm_area_struct *rc_vma;
> > + unsigned long rc_vaddr;
> > + int ret = 0;
> > +
> > + rc_vma = find_ref_ctr_vma(uprobe, mm);
> > +
> > + if (rc_vma) {
> > + rc_vaddr = offset_to_vaddr(rc_vma, uprobe->ref_ctr_offset);
> > + ret = __update_ref_ctr(mm, rc_vaddr, is_register ? 1 : -1);
> > +
> > + if (is_register)
> > + return ret;
> > + }
> Mixing __update_ref_ctr() here and delayed_uprobe_add() in the same
> function is a little confusing (at least for me). How about we always use
> delayed uprobe for uprobe_mmap() and use non-delayed in other case(s)?
>
> > +
> > + mutex_lock(&delayed_uprobe_lock);
> > + if (is_register)
> > + ret = delayed_uprobe_add(uprobe, mm);
> > + else
> > + delayed_uprobe_remove(uprobe, mm);
> > + mutex_unlock(&delayed_uprobe_lock);
> > +
> > + return ret;
> > +}
> > +
> > /*
> > * NOTE:
> > * Expect the breakpoint instruction to be the smallest size instruction for
> > @@ -302,9 +463,13 @@ static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t
> > int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> > unsigned long vaddr, uprobe_opcode_t opcode)
> > {
> > + struct uprobe *uprobe;
> > struct page *old_page, *new_page;
> > struct vm_area_struct *vma;
> > - int ret;
> > + int ret, is_register, ref_ctr_updated = 0;
> > +
> > + is_register = is_swbp_insn(&opcode);
> > + uprobe = container_of(auprobe, struct uprobe, arch);
> >
> > retry:
> > /* Read the page with vaddr into memory */
> > @@ -317,6 +482,15 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> > if (ret <= 0)
> > goto put_old;
> >
> > + /* We are going to replace instruction, update ref_ctr. */
> > + if (!ref_ctr_updated && uprobe->ref_ctr_offset) {
> > + ret = update_ref_ctr(uprobe, mm, is_register);
> > + if (ret)
> > + goto put_old;
> > +
> > + ref_ctr_updated = 1;
> > + }
> > +
> > ret = anon_vma_prepare(vma);
> > if (ret)
> > goto put_old;
> > @@ -337,6 +511,11 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> >
> > if (unlikely(ret == -EAGAIN))
> > goto retry;
> > +
> > + /* Revert back reference counter if instruction update failed. */
> > + if (ret && is_register && ref_ctr_updated)
> > + update_ref_ctr(uprobe, mm, false);
> > +
> > return ret;
> > }
> >
> > @@ -378,8 +557,15 @@ static struct uprobe *get_uprobe(struct uprobe *uprobe)
> >
> > static void put_uprobe(struct uprobe *uprobe)
> > {
> > - if (atomic_dec_and_test(&uprobe->ref))
> > + if (atomic_dec_and_test(&uprobe->ref)) {
> > + /*
> > + * If application munmap(exec_vma) before uprobe_unregister()
> > + * gets called, we don't get a chance to remove uprobe from
> > + * delayed_uprobe_list in remove_breakpoint(). Do it here.
> > + */
> > + delayed_uprobe_remove(uprobe, NULL);
> > kfree(uprobe);
> > + }
> > }
> >
> > static int match_uprobe(struct uprobe *l, struct uprobe *r)
> > @@ -484,7 +670,8 @@ static struct uprobe *insert_uprobe(struct uprobe *uprobe)
> > return u;
> > }
> >
> > -static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
> > +static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
> > + loff_t ref_ctr_offset)
> > {
> > struct uprobe *uprobe, *cur_uprobe;
> >
> > @@ -494,6 +681,7 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
> >
> > uprobe->inode = inode;
> > uprobe->offset = offset;
> > + uprobe->ref_ctr_offset = ref_ctr_offset;
> > init_rwsem(&uprobe->register_rwsem);
> > init_rwsem(&uprobe->consumer_rwsem);
> >
> > @@ -895,7 +1083,7 @@ EXPORT_SYMBOL_GPL(uprobe_unregister);
> > * else return 0 (success)
> > */
> > static int __uprobe_register(struct inode *inode, loff_t offset,
> > - struct uprobe_consumer *uc)
> > + loff_t ref_ctr_offset, struct uprobe_consumer *uc)
> > {
> > struct uprobe *uprobe;
> > int ret;
> > @@ -912,7 +1100,7 @@ static int __uprobe_register(struct inode *inode, loff_t offset,
> > return -EINVAL;
> >
> > retry:
> > - uprobe = alloc_uprobe(inode, offset);
> > + uprobe = alloc_uprobe(inode, offset, ref_ctr_offset);
> > if (!uprobe)
> > return -ENOMEM;
> > /*
> > @@ -938,10 +1126,17 @@ static int __uprobe_register(struct inode *inode, loff_t offset,
> > int uprobe_register(struct inode *inode, loff_t offset,
> > struct uprobe_consumer *uc)
> > {
> > - return __uprobe_register(inode, offset, uc);
> > + return __uprobe_register(inode, offset, 0, uc);
> > }
> > EXPORT_SYMBOL_GPL(uprobe_register);
> >
> > +int uprobe_register_refctr(struct inode *inode, loff_t offset,
> > + loff_t ref_ctr_offset, struct uprobe_consumer *uc)
> > +{
> > + return __uprobe_register(inode, offset, ref_ctr_offset, uc);
> > +}
> > +EXPORT_SYMBOL_GPL(uprobe_register_refctr);
> > +
> > /*
> > * uprobe_apply - unregister a already registered probe.
> > * @inode: the file in which the probe has to be removed.
> > @@ -1060,6 +1255,31 @@ static void build_probe_list(struct inode *inode,
> > spin_unlock(&uprobes_treelock);
> > }
> >
> > +static int delayed_uprobe_install(struct vm_area_struct *vma)
> This function name is confusing. How about we call it delayed_ref_ctr_incr() or
> something similar? Also, we should add comments to highlight this is vma is not
> the vma containing the uprobe, but the vma containing the ref_ctr.
>
> > +{
> > + struct list_head *pos, *q;
> > + struct delayed_uprobe *du;
> > + unsigned long vaddr;
> > + int ret = 0, err = 0;
> > +
> > + mutex_lock(&delayed_uprobe_lock);
> > + list_for_each_safe(pos, q, &delayed_uprobe_list) {
> > + du = list_entry(pos, struct delayed_uprobe, list);
> > +
> > + if (!valid_ref_ctr_vma(du->uprobe, vma))
> > + continue;
> > +
> > + vaddr = offset_to_vaddr(vma, du->uprobe->ref_ctr_offset);
> > + ret = __update_ref_ctr(vma->vm_mm, vaddr, 1);
> > + /* Record an error and continue. */
> > + if (ret && !err)
> > + err = ret;
> I think this is a good place (when ret != 0) to call pr_warn(). I guess we can
> print which mm get error for which uprobe (inode+offset).
>
> > + delayed_uprobe_delete(du);
> > + }
> > + mutex_unlock(&delayed_uprobe_lock);
> > + return err;
> > +}
> > +
> > /*
> > * Called from mmap_region/vma_adjust with mm->mmap_sem acquired.
> > *
> > @@ -1072,7 +1292,15 @@ int uprobe_mmap(struct vm_area_struct *vma)
> > struct uprobe *uprobe, *u;
> > struct inode *inode;
> >
> > - if (no_uprobe_events() || !valid_vma(vma, true))
> > + if (no_uprobe_events())
> > + return 0;
> > +
> > + if (vma->vm_file &&
> > + (vma->vm_flags & (VM_WRITE|VM_SHARED)) == VM_WRITE &&
> > + test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags))
> > + delayed_uprobe_install(vma);
> > +
> > + if (!valid_vma(vma, true))
> > return 0;
> >
> > inode = file_inode(vma->vm_file);
> > @@ -1246,6 +1474,10 @@ void uprobe_clear_state(struct mm_struct *mm)
> > {
> > struct xol_area *area = mm->uprobes_state.xol_area;
> >
> > + mutex_lock(&delayed_uprobe_lock);
> > + delayed_uprobe_remove(NULL, mm);
> > + mutex_unlock(&delayed_uprobe_lock);
> > +
> > if (!area)
> > return;
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 823687997b01..616160b85860 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -4620,7 +4620,7 @@ static const char readme_msg[] =
> > "place (kretprobe): [<module>:]<symbol>[+<offset>]|<memaddr>\n"
> > #endif
> > #ifdef CONFIG_UPROBE_EVENTS
> > - "\t place: <path>:<offset>\n"
> > + " place (uprobe): <path>:<offset>[(ref_ctr_offset)]\n"
> > #endif
> > "\t args: <name>=fetcharg[:type]\n"
> > "\t fetcharg: %<register>, @ , @<symbol>[+|-<offset>],\n"
> > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> > index bf89a51e740d..bf2be098eb08 100644
> > --- a/kernel/trace/trace_uprobe.c
> > +++ b/kernel/trace/trace_uprobe.c
> > @@ -59,6 +59,7 @@ struct trace_uprobe {
> > struct inode *inode;
> > char *filename;
> > unsigned long offset;
> > + unsigned long ref_ctr_offset;
> > unsigned long nhit;
> > struct trace_probe tp;
> > };
> > @@ -364,10 +365,10 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
> > static int create_trace_uprobe(int argc, char **argv)
> > {
> > struct trace_uprobe *tu;
> > - char *arg, *event, *group, *filename;
> > + char *arg, *event, *group, *filename, *rctr, *rctr_end;
> > char buf[MAX_EVENT_NAME_LEN];
> > struct path path;
> > - unsigned long offset;
> > + unsigned long offset, ref_ctr_offset;
> > bool is_delete, is_return;
> > int i, ret;
> >
> > @@ -376,6 +377,7 @@ static int create_trace_uprobe(int argc, char **argv)
> > is_return = false;
> > event = NULL;
> > group = NULL;
> > + ref_ctr_offset = 0;
> >
> > /* argc must be >= 1 */
> > if (argv[0][0] == '-')
> > @@ -450,6 +452,26 @@ static int create_trace_uprobe(int argc, char **argv)
> > goto fail_address_parse;
> > }
> >
> > + /* Parse reference counter offset if specified. */
> > + rctr = strchr(arg, '(');
> > + if (rctr) {
> > + rctr_end = strchr(rctr, ')');
> > + if (rctr > rctr_end || *(rctr_end + 1) != 0) {
> > + ret = -EINVAL;
> > + pr_info("Invalid reference counter offset.\n");
> > + goto fail_address_parse;
> > + }
> > +
> > + *rctr++ = '\0';
> > + *rctr_end = '\0';
> > + 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;
> > @@ -484,6 +506,7 @@ static int create_trace_uprobe(int argc, char **argv)
> > goto fail_address_parse;
> > }
> > tu->offset = offset;
> > + tu->ref_ctr_offset = ref_ctr_offset;
> > tu->path = path;
> > tu->filename = kstrdup(filename, GFP_KERNEL);
> >
> > @@ -602,6 +625,9 @@ static int probes_seq_show(struct seq_file *m, void *v)
> > trace_event_name(&tu->tp.call), tu->filename,
> > (int)(sizeof(void *) * 2), tu->offset);
> >
> > + 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);
> >
> > @@ -917,7 +943,13 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
> >
> > tu->consumer.filter = filter;
> > tu->inode = d_real_inode(tu->path.dentry);
> > - ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> > + if (tu->ref_ctr_offset) {
> > + ret = uprobe_register_refctr(tu->inode, tu->offset,
> > + tu->ref_ctr_offset, &tu->consumer);
> > + } else {
> > + ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> > + }
> > +
> > if (ret)
> > goto err_buffer;
> >
> > --
> > 2.14.4
> >