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>

4 files changed, 12 insertions, 8 deletions

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index d594d3b3ad4c..efe4b3308c74 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -107,7 +107,7 @@ extern bool __weak is_swbp_insn(uprobe_opcode_t *insn);
 extern int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
 extern void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
 extern int uprobe_mmap(struct vm_area_struct *vma);
-extern void uprobe_munmap(struct vm_area_struct *vma);
+extern void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end);
 extern void uprobe_free_utask(struct task_struct *t);
 extern void uprobe_copy_process(struct task_struct *t);
 extern unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs);
@@ -134,7 +134,8 @@ static inline int uprobe_mmap(struct vm_area_struct *vma)
 {
         return 0;
 }
-static inline void uprobe_munmap(struct vm_area_struct *vma)
+static inline void
+uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
 {
 }
 static inline void uprobe_notify_resume(struct pt_regs *regs)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c5caeecea1dc..985be4d80fe8 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.
diff --git a/mm/memory.c b/mm/memory.c
index 6105f475fa86..bf8b4035277d 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 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);