[Tarantool-patches] [PATCH luajit 1/2] Fix handling of errors during snapshot restore.
sergos
sergos at tarantool.org
Mon Aug 1 12:38:15 MSK 2022
Hi!
Thanks for the patch!
With some comments fixes LGTM.
Sergos
> On 31 Jul 2022, at 13:58, Sergey Kaplun <skaplun at tarantool.org> wrote:
>
> From: Mike Pall <mike>
>
> (cherry picked from commit 12ab596997b9cb27846a5b254d11230c3f9c50c8)
>
> When an error is raised during snapshot restore, `err_unwind()` skipped the
the the
> correct cframe to stop unwinding. It happens due this frame is C frame
that should stop The reason is a
> without Lua frame and the special negative value of `cfram_nres()` for
^^^^^^^ ^e
not sure if I got it right - wrapping frame? Anyways an article is missing
> this frame isn't set.
>
> This patch sets `cframe_nres()` for cframe with snap restoration to
the a that contains a
> `-2*LUAI_MAXSTACK` to guarantee that an error will be always caught
> here.
Not quite clear why this should be done always, since you mentioned before the
Lua frame presence mitigates the problem. Does it mean the cframe_nres() is
ignored if Lua frame is present? Mention it if it is true.
>
> Sergey Kaplun:
> * added the description and the test for the problem
>
> Part of tarantool/tarantool#7230
> ---
> src/lj_trace.c | 2 ++
> .../lj-603-err-snap-restore.test.lua | 30 +++++++++++++++++++
> 2 files changed, 32 insertions(+)
> create mode 100644 test/tarantool-tests/lj-603-err-snap-restore.test.lua
>
> diff --git a/src/lj_trace.c b/src/lj_trace.c
> index d7a78d4d..68a657a7 100644
> --- a/src/lj_trace.c
> +++ b/src/lj_trace.c
> @@ -803,6 +803,8 @@ static TValue *trace_exit_cp(lua_State *L, lua_CFunction dummy, void *ud)
> {
> ExitDataCP *exd = (ExitDataCP *)ud;
> cframe_errfunc(L->cframe) = -1; /* Inherit error function. */
> + /* Always catch error here. */
> + cframe_nres(L->cframe) = -2*LUAI_MAXSTACK*(int)sizeof(TValue);
> exd->pc = lj_snap_restore(exd->J, exd->exptr);
> UNUSED(dummy);
> return NULL;
> diff --git a/test/tarantool-tests/lj-603-err-snap-restore.test.lua b/test/tarantool-tests/lj-603-err-snap-restore.test.lua
> new file mode 100644
> index 00000000..82ce6a8f
> --- /dev/null
> +++ b/test/tarantool-tests/lj-603-err-snap-restore.test.lua
> @@ -0,0 +1,30 @@
> +local tap = require('tap')
> +
> +-- Test file to demonstrate the incorrect JIT behaviour when an
???
> +-- error is raised on restoration from the snapshot.
> +-- See also https://github.com/LuaJIT/LuaJIT/issues/603.
> +local test = tap.test('lj-603-err-snap-restore.test.lua')
> +test:plan(1)
> +
> +local recursive_f
> +local function errfunc()
> + xpcall(recursive_f, errfunc)
> +end
> +
> +-- A recursive call to itself leads to trace with up-recursion.
> +-- When the Lua stack can't be grown more, error is raised on
> +-- restoration from the snapshot.
> +recursive_f = function()
> + xpcall(recursive_f, errfunc)
> + errfunc = function() end
> + recursive_f = function() end
> +end
> +recursive_f()
> +
> +test:ok(true)
> +
> +-- XXX: Don't use `os.exit()` here intense. When error on snap
^^^ explicitly? | by intention?
> +-- restoration is raised, `err_unwind()` doesn't stop on correct
> +-- cframe. So later, on exit from VM this corrupted cframe chain
> +-- shows itself. `os.exit()` literally calls `exit()` and doesn't
> +-- show the issue.
> --
> 2.34.1
>
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