* Ingo Molnar [off-list ref] [2012-01-16 09:34:42]:

* Srikar Dronamraju [off-list ref] wrote:

quoted

This patchset implements Uprobes which enables you to 
dynamically probe any routine in a user space application and 
collect information non-disruptively.

Did all review feedback get addressed in your latest tree?

I think this question would be better answered by Peter, Oleg and
Masami.  For my part, I have fixed all comments till now.  Also uprobes
has been part of -next for quite sometime.

If yes then it would be nice to hear the opinion of Andrew about 
this bit:

quoted

 mm/mmap.c                               |   33 +-

The relevant portion of the patch is:

quoted

--- a/mm/mmap.c
+++ b/mm/mmap.c

@@ -30,6 +30,7 @@
 #include <linux/perf_event.h>
 #include <linux/audit.h>
 #include <linux/khugepaged.h>
+#include <linux/uprobes.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>

@@ -616,6 +617,13 @@ again:			remove_next = 1 + (end > next->vm_end);
 	if (mapping)
 		mutex_unlock(&mapping->i_mmap_mutex);
 
+	if (root) {
+		mmap_uprobe(vma);
+
+		if (adjust_next)
+			mmap_uprobe(next);
+	}
+
 	if (remove_next) {
 		if (file) {
 			fput(file);

@@ -637,6 +645,8 @@ again:			remove_next = 1 + (end > next->vm_end);
 			goto again;
 		}
 	}
+	if (insert && file)
+		mmap_uprobe(insert);
 
 	validate_mm(mm);
 

@@ -1329,6 +1339,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 			mm->locked_vm += (len >> PAGE_SHIFT);
 	} else if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK))
 		make_pages_present(addr, addr + len);
+
+	if (file && mmap_uprobe(vma))
+		/* matching probes but cannot insert */
+		goto unmap_and_free_vma;
+
 	return addr;
 
 unmap_and_free_vma:

@@ -2305,6 +2320,10 @@ int insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
 	if ((vma->vm_flags & VM_ACCOUNT) &&
 	     security_vm_enough_memory_mm(mm, vma_pages(vma)))
 		return -ENOMEM;
+
+	if (vma->vm_file && mmap_uprobe(vma))
+		return -EINVAL;
+
 	vma_link(mm, vma, prev, rb_link, rb_parent);
 	return 0;
 }

@@ -2356,6 +2375,10 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 			new_vma->vm_pgoff = pgoff;
 			if (new_vma->vm_file) {
 				get_file(new_vma->vm_file);
+
+				if (mmap_uprobe(new_vma))
+					goto out_free_mempol;
+
 				if (vma->vm_flags & VM_EXECUTABLE)
 					added_exe_file_vma(mm);
 			}

it's named mmap_uprobe(), which makes it rather single-purpose. 
The uprobes code wants to track vma life-time so that it can 
manage uprobes breakpoints installed here, correct?

Yes, 

We already have some other vma tracking goodies in perf itself 
(see perf_event_mmap() et al) - would it make sense to merge the 
two vma instrumentation facilities and not burden mm/ with two 
separate sets of callbacks?

Atleast for file backed vmas, perf_event_mmap seems to be interested in
just the new vma creations. Uprobes would also be interested in the size
changes like the vma growing/shrinking/remap. Is perf_event_mmap
interested in such changes? From what i could see, perf_event_mmap seems
to be interested in stack vma size changes but not file vma size
changes.

Also mmap_uprobe gets called in fork path. Currently we have a hook in
copy_mm/dup_mm so that we get to know the context of each vma that gets
added to the child and add its breakpoints. At dup_mm/dup_mmap we would
have taken mmap_sem for both parent and child so there is no way we
could have missed a register/unregister in the parent not reflected in
the child.

I see the perf_event_fork but that would have to enhanced to do a lot
more to help us do a mmap_uprobe.

If all such issues are resolved then i guess we could queue up 
uprobes in -tip, conditional on it remaining sufficiently 
regression-, problem- and NAK-free.

Okay. Accepting uprobes into tip, would provide more testing/feedback.

Also, it would be nice to hear Arnaldo's opinion about the 
tools/perf/ bits.

Whatever comments Arnaldo/Masami have given till now have been resolved.

-- 
Thanks and Regards
Srikar

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