[PATCH 2/3] uprobes: change build_map_info() to try kmalloc(GFP_NOWAIT) first

[Oleg Nesterov <oleg@redhat.com>]

build_map_info() doesn't allocate the memory under i_mmap_mutex
to avoid the deadlock with page reclaim. But it can try GFP_NOWAIT
first, it should work in the likely case and thus we almost never
need the pre-alloc-and-retry path.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/events/uprobes.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index a1bbcab..c9836ae 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -772,8 +772,13 @@ build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
 			continue;
 
 		if (!prev) {
-			more++;
-			continue;
+			prev = kmalloc(sizeof(struct map_info),
+					GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			if (!prev) {
+				more++;
+				continue;
+			}
+			prev->next = NULL;
 		}
 
 		if (!atomic_inc_not_zero(&vma->vm_mm->mm_users))
-- 
1.5.5.1