uprobes: Change build_map_info() to try kmalloc(GFP_NOWAIT) first

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 <[email protected]> Acked-by: Srikar Dronamraju <[email protected]> Acked-by: Peter Zijlstra <[email protected]> Cc: Ananth N Mavinakayanahalli <[email protected]> Cc: Anton Arapov <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]>
mna · Jun 16, 2012 · 7a5bfb6 · 7a5bfb6
1 parent 2687209
commit 7a5bfb6
Showing 1 changed file with 10 additions and 0 deletions.
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
@@ -761,6 +761,16 @@ build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
 		if (!valid_vma(vma, is_register))
 			continue;
 
+		if (!prev && !more) {
+			/*
+			 * Needs GFP_NOWAIT to avoid i_mmap_mutex recursion through
+			 * reclaim. This is optimistic, no harm done if it fails.
+			 */
+			prev = kmalloc(sizeof(struct map_info),
+					GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			if (prev)
+				prev->next = NULL;
+		}
 		if (!prev) {
 			more++;
 			continue;