uprobes/core: Decrement uprobe count before the pages are unmapped

Uprobes has a callback (uprobe_munmap()) in the unmap path to
maintain the uprobes count.

In the exit path this callback gets called in unlink_file_vma().
However by the time unlink_file_vma() is called, the pages would
have been unmapped (in unmap_vmas()) and the task->rss_stat counts
accounted (in zap_pte_range()).

If the exiting process has probepoints, uprobe_munmap() checks if
the breakpoint instruction was around before decrementing the probe
count.

This results in a file backed page being reread by uprobe_munmap()
and hence it does not find the breakpoint.

This patch fixes this problem by moving the callback to
unmap_single_vma(). Since unmap_single_vma() may not unmap the
complete vma, add start and end parameters to uprobe_munmap().

This bug became apparent courtesy of commit c3f0327f8e9d
("mm: add rss counters consistency check").

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Linux-mm <linux-mm@kvack.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120411103527.23245.9835.sendpatchset@srdronam.in.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 7 insertions, 4 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 6105f47..bf8b403 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1307,6 +1307,9 @@ static void unmap_single_vma(struct mmu_gather *tlb,
 	if (end <= vma->vm_start)
 		return;
 
+	if (vma->vm_file)
+		uprobe_munmap(vma, start, end);
+
 	if (vma->vm_flags & VM_ACCOUNT)
 		*nr_accounted += (end - start) >> PAGE_SHIFT;
 
diff --git a/mm/mmap.c b/mm/mmap.c
index b17a39f..15c21a1 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -218,7 +218,6 @@ void unlink_file_vma(struct vm_area_struct *vma)
 		mutex_lock(&mapping->i_mmap_mutex);
 		__remove_shared_vm_struct(vma, file, mapping);
 		mutex_unlock(&mapping->i_mmap_mutex);
-		uprobe_munmap(vma);
 	}
 }
 
@@ -548,10 +547,11 @@ again:			remove_next = 1 + (end > next->vm_end);
 		mapping = file->f_mapping;
 		if (!(vma->vm_flags & VM_NONLINEAR)) {
 			root = &mapping->i_mmap;
-			uprobe_munmap(vma);
+			uprobe_munmap(vma, vma->vm_start, vma->vm_end);
 
 			if (adjust_next)
-				uprobe_munmap(next);
+				uprobe_munmap(next, next->vm_start,
+							next->vm_end);
 		}
 
 		mutex_lock(&mapping->i_mmap_mutex);
@@ -632,7 +632,7 @@ again:			remove_next = 1 + (end > next->vm_end);
 
 	if (remove_next) {
 		if (file) {
-			uprobe_munmap(next);
+			uprobe_munmap(next, next->vm_start, next->vm_end);
 			fput(file);
 			if (next->vm_flags & VM_EXECUTABLE)
 				removed_exe_file_vma(mm);