linux-kernel - Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference count (semaphore)

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Date:   Fri, 16 Mar 2018 17:16:17 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        mhiramat@...nel.org, peterz@...radead.org,
        srikar@...ux.vnet.ibm.com, acme@...nel.org,
        ananth@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
        alexander.shishkin@...ux.intel.com, alexis.berlemont@...il.com,
        corbet@....net, dan.j.williams@...el.com,
        gregkh@...uxfoundation.org, huawei.libin@...wei.com,
        hughd@...gle.com, jack@...e.cz, jglisse@...hat.com,
        jolsa@...hat.com, kan.liang@...el.com,
        kirill.shutemov@...ux.intel.com, kjlx@...pleofstupid.com,
        kstewart@...uxfoundation.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
        milian.wolff@...b.com, mingo@...hat.com, namhyung@...nel.org,
        naveen.n.rao@...ux.vnet.ibm.com, pc@...ibm.com,
        pombredanne@...b.com, tglx@...utronix.de,
        tmricht@...ux.vnet.ibm.com, willy@...radead.org,
        yao.jin@...ux.intel.com, fengguang.wu@...el.com
Subject: Re: [PATCH 5/8] trace_uprobe: Support SDT markers having reference
 count (semaphore)

On 03/15, Steven Rostedt wrote:
>
> On Tue, 13 Mar 2018 18:26:00 +0530
> Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> wrote:
>
> > +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();
>
> Please add a comment here that this function ups the mm ref count for
> each info returned. Otherwise it's hard to know what that mmput() below
> matches.

You meant uprobe_build_map_info(), not uprobe_start_dup_mmap().

Yes, and if it gets more callers perhaps we should move this mmput() into
uprobe_free_map_info()...

Oleg.


--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -714,6 +714,7 @@ struct map_info {
 static inline struct map_info *free_map_info(struct map_info *info)
 {
 	struct map_info *next = info->next;
+	mmput(info->mm);
 	kfree(info);
 	return next;
 }
@@ -783,8 +784,11 @@ build_map_info(struct address_space *map
 
 	goto again;
  out:
-	while (prev)
-		prev = free_map_info(prev);
+	while (prev) {
+		info = prev;
+		prev = prev->next;
+		kfree(info);
+	}
 	return curr;
 }
 
@@ -834,7 +838,6 @@ register_for_each_vma(struct uprobe *upr
  unlock:
 		up_write(&mm->mmap_sem);
  free:
-		mmput(mm);
 		info = free_map_info(info);
 	}
  out: