[Tarantool-patches] [PATCH v5 2/2] fiber: leak slab if unable to bring prots back

[Cyrill Gorcunov]

In case if we unable to revert guard page back to
read|write we should never use such slab again.

Initially I thought of just put panic here and
exit but it is too destructive. I think better
print an error and continue. If node admin ignore
this message then one moment at future there won't
be slab left for use and creating new fibers get
prohibited.

In future (hopefully near one) we plan to drop
guard pages to prevent VMA fracturing and use
stack marks instead.

Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
---
 src/lib/core/fiber.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
index 57e4cb6ef..5298541d4 100644
--- a/src/lib/core/fiber.c
+++ b/src/lib/core/fiber.c
@@ -1055,15 +1055,21 @@ fiber_stack_destroy(struct fiber *fiber, struct slab_cache *slabc)
 			 * to setup the original protection back in
 			 * background.
 			 *
+			 * For now lets keep such slab referenced and
+			 * leaked: if mprotect failed we must not allow
+			 * to reuse such slab with PROT_NONE'ed page
+			 * inside.
+			 *
 			 * Note that in case if we're called from
 			 * fiber_stack_create() the @mprotect_flags is
 			 * the same as the slab been created with, so
 			 * calling mprotect for VMA with same flags
 			 * won't fail.
 			 */
-			diag_log();
-		}
-		slab_put(slabc, fiber->stack_slab);
+			say_syserror("fiber: Can't put guard page to slab. "
+				     "Leak %zu bytes", (size_t)fiber->stack_size);
+		} else
+			slab_put(slabc, fiber->stack_slab);
 	}
 }
 
-- 
2.20.1