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, 4 insertions, 4 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index b17a39f31a5e..15c21a150402 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);