From: Maksim Kokryashkin via Tarantool-patches <tarantool-patches@dev.tarantool.org> To: tarantool-patches@dev.tarantool.org, sergeyb@tarantool.org, skaplun@tarantool.org, m.kokryashkin@tarantool.org Subject: [Tarantool-patches] [PATCH luajit] sysprof: disable runtime host symtab updates Date: Fri, 8 Dec 2023 09:10:23 +0300 [thread overview] Message-ID: <20231208061023.89512-1-max.kokryashkin@gmail.com> (raw) From: Maxim Kokryashkin <m.kokryashkin@tarantool.org> The symtab update for newly loaded shared libraries requires memory allocation, which is not signal-safe and can cause crashes. Updating symtab in a VM hook is not a viable option either, as there are no guarantees that the symbol will be dumped before its address is streamed. This patch completely disables the runtime updates of the symtab for host symbols. That means all Lua-C modules, FFI modules, and shared libraries must be loaded before starting the profiler. There is no test along with the patch for two main reasons: 1. The signal should land on an instruction inside the allocator such that the second allocator call would cause a crash because of an inconsistent inner state. Although we have ptrace-based machinery for testing, the control is not that fine-grained. The only option we have left is to rely on empirical offsets, which is not a robust solution. Moreover, it is possible to build LuaJIT with `malloc` as an allocator, and the test should be adapted to that too. Needless to say, malloc sources may differ from platform to platform, making the test unreliable. 2. Regression is unlikely here since this patch removes the only call that could allocate memory inside the signal handler. Resolves tarantool/tarantool#8140 --- Branch: https://github.com/tarantool/luajit/tree/fckxorg/gh-8140-crash-in-allocator Issue: https://github.com/tarantool/tarantool/issues/8140 PR: https://github.com/tarantool/tarantool/pull/9460 src/lj_sysprof.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/src/lj_sysprof.c b/src/lj_sysprof.c index c6c20de2..88c7a41b 100644 --- a/src/lj_sysprof.c +++ b/src/lj_sysprof.c @@ -75,7 +75,6 @@ struct sysprof { luam_Sysprof_backtracer backtracer; /* Backtracing function for the host stack. */ lj_profile_timer timer; /* Profiling timer. */ int saved_errno; /* Saved errno when profiler failed. */ - uint32_t lib_adds; /* Number of libs loaded. Monotonic. */ }; /* ** XXX: Only one VM can be profiled at a time. @@ -100,7 +99,11 @@ static int is_unconfigured(struct sysprof *sp) static void stream_prologue(struct sysprof *sp) { - lj_symtab_dump(&sp->out, sp->g, &sp->lib_adds); + /* + ** XXX: Must be zero for the symtab module to dump all loaded libraries. + */ + uint32_t unused_lib_adds = 0; + lj_symtab_dump(&sp->out, sp->g, &unused_lib_adds); lj_wbuf_addn(&sp->out, ljp_header, sizeof(ljp_header)); } @@ -256,8 +259,6 @@ static void stream_guest(struct sysprof *sp, uint32_t vmstate) static void stream_host(struct sysprof *sp, uint32_t vmstate) { - struct lua_State *L = gco2th(gcref(sp->g->cur_L)); - lj_symtab_dump_newc(&sp->lib_adds, &sp->out, LJP_SYMTAB_CFUNC_EVENT, L); lj_wbuf_addbyte(&sp->out, (uint8_t)vmstate); stream_backtrace_host(sp); } -- 2.39.3 (Apple Git-145)
next reply other threads:[~2023-12-08 6:10 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-12-08 6:10 Maksim Kokryashkin via Tarantool-patches [this message] 2023-12-12 9:46 ` Sergey Kaplun via Tarantool-patches 2023-12-29 13:05 ` Sergey Bronnikov via Tarantool-patches 2024-02-15 13:40 ` Igor Munkin via Tarantool-patches
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