[Tarantool-patches] [PATCH v2 2/2] fiber: exit with panic if we unable to revert guard page

[Cyrill Gorcunov]

At the moment we setup fiber's stack with a guard page
which is used to detect stack overrun. This page is just
a regular page taken from a slab with PROT_NONE attribute.

Once fiber is no longer needed we try to revert this
attribute back to PROT_READ | PROT_WRITE. Still there
is a pretty small chance that this attempt get failed.

Thus in such case we should not allow to proceed but rather
lets panic, otherwise the slab won't longer be solid r/w memory
area and attempt to write into this page will cause
an unpredictable exception.

Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
---
 src/lib/core/fiber.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
index b51f46f2f..fdad7607c 100644
--- a/src/lib/core/fiber.c
+++ b/src/lib/core/fiber.c
@@ -1041,13 +1041,17 @@ fiber_stack_destroy(struct fiber *fiber, struct slab_cache *slabc)
 			 * to setup the original protection back in
 			 * background.
 			 *
+			 * For now lets exit with panic: if mprotect
+			 * failed we must not allow to reuse such slab
+			 * with PROT_NONE'ed page somewhere 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();
+			panic_syserror("fiber: Can't put guard page to slab");
 		}
 		slab_put(slabc, fiber->stack_slab);
 	}
-- 
2.20.1