[Tarantool-patches] [PATCH v6 2/2] fiber: leak slab if unable to bring prots back
Vladislav Shpilevoy
v.shpilevoy at tarantool.org
Thu Feb 13 03:08:45 MSK 2020
Thanks for the patch!
On 06/02/2020 13:31, Cyrill Gorcunov wrote:
> 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.
>
> Reviewed-by: Alexander Turenko <alexander.turenko at tarantool.org>
> Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
> ---
> src/lib/core/fiber.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
> index 57e4cb6ef..a501d846a 100644
> --- a/src/lib/core/fiber.c
> +++ b/src/lib/core/fiber.c
> @@ -1055,15 +1055,22 @@ 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();
> + say_syserror("fiber: Can't put guard page to slab. "
> + "Leak %zu bytes", (size_t)fiber->stack_size);
This behaviour actually should be testable, no? You could not test
diag, but you should be able to detect a leak. Using slab_cache_used(),
for example. Before and after a test.
> + } else {
> + slab_put(slabc, fiber->stack_slab);
> }
> - slab_put(slabc, fiber->stack_slab);
> }
> }
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