uprobes: share the i_mmap_rwsem

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>
Acked-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 1901dbf..995a95f 100644 (file)
--- 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;