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>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c5caeec..985be4d 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1112,7 +1112,7 @@ int uprobe_mmap(struct vm_area_struct *vma)
 /*
  * Called in context of a munmap of a vma.
  */
-void uprobe_munmap(struct vm_area_struct *vma)
+void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
 {
 	struct list_head tmp_list;
 	struct uprobe *uprobe, *u;
@@ -1138,7 +1138,7 @@ void uprobe_munmap(struct vm_area_struct *vma)
 		list_del(&uprobe->pending_list);
 		vaddr = vma_address(vma, uprobe->offset);
 
-		if (vaddr >= vma->vm_start && vaddr < vma->vm_end) {
+		if (vaddr >= start && vaddr < end) {
 			/*
 			 * An unregister could have removed the probe before
 			 * unmap. So check before we decrement the count.