[PATCH 05/10] uprobes: share the i_mmap_rwsem

[Davidlohr Bueso <dave@stgolabs.net>]

Both register and unregister call build_map_info() in order
to create the list of mappings before installing or removing
breakpoints for every mm which maps file backed memory. As
such, there is no reason to hold the i_mmap_rwsem exclusively,
so share it and allow concurrent readers to build the mapping
data.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@intel.linux.com>
---
 kernel/events/uprobes.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index e1bb60d..6158a64b 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -724,7 +724,7 @@ build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
 	int more = 0;
 
  again:
-	i_mmap_lock_write(mapping);
+	i_mmap_lock_read(mapping);
 	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
 		if (!valid_vma(vma, is_register))
 			continue;
@@ -755,7 +755,7 @@ build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
 		info->mm = vma->vm_mm;
 		info->vaddr = offset_to_vaddr(vma, offset);
 	}
-	i_mmap_unlock_write(mapping);
+	i_mmap_unlock_read(mapping);
 
 	if (!more)
 		goto out;
-- 
1.8.4.5