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DEBUG: lua: add tainted flags for stuck Lua contexts

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William suggested that since we can detect the presence of Lua in the
stack, let's combine it with stuck detection to set a new pair of flags
indicating a stuck Lua context and a stuck Lua shared context.

Now, executing an infinite loop in a Lua sample fetch function with
yield disabled crashes with tainted=0xe40 if loaded from a lua-load
statement, or tainted=0x640 from a lua-load-per-thread statement.

In addition, at the end of the panic dump, we can check if Lua was
seen stuck and emit recommendations about lua-load-per-thread and
the choice of dependencies depending on the presence of threads
and/or shared context.
This commit is contained in:
Willy Tarreau 2023-10-25 15:02:59 +02:00
parent 46bbb3a33b
commit 26a6481f00
2 changed files with 34 additions and 0 deletions
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2
include/haproxy/bug.h
View File

@ -249,6 +249,8 @@ enum tainted_flags {
TAINTED_REDEFINITION = 0x00000080, /* symbol redefinition detected */
TAINTED_REPLACED_MEM_ALLOCATOR = 0x00000100, /* memory allocator was replaced using LD_PRELOAD */
TAINTED_PANIC = 0x00000200, /* a panic dump has started */
TAINTED_LUA_STUCK = 0x00000400, /* stuck in a Lua context */
TAINTED_LUA_STUCK_SHARED = 0x00000800, /* stuck in a shared Lua context */
};
/* this is a bit field made of TAINTED_*, and is declared in haproxy.c */

32
src/debug.c
View File

@ -227,6 +227,19 @@ void ha_thread_dump_one(int thr, int from_signal)
ha_task_dump(buf, th_ctx->current, " ");
if (stuck && thr == tid) {
#ifdef USE_LUA
if (th_ctx->current &&
th_ctx->current->process == process_stream && th_ctx->current->context) {
const struct stream *s = (const struct stream *)th_ctx->current->context;
struct hlua *hlua = s ? s->hlua : NULL;
if (hlua && hlua->T) {
mark_tainted(TAINTED_LUA_STUCK);
if (hlua->state_id == 0)
mark_tainted(TAINTED_LUA_STUCK_SHARED);
}
}
#endif
/* We only emit the backtrace for stuck threads in order not to
* waste precious output buffer space with non-interesting data.
* Please leave this as the last instruction in this function
@ -437,6 +450,25 @@ void ha_panic()
chunk_reset(&trash);
}
#ifdef USE_LUA
if (get_tainted() & TAINTED_LUA_STUCK_SHARED && global.nbthread > 1) {
chunk_printf(&trash,
"### Note: at least one thread was stuck in a Lua context loaded using the\n"
" 'lua-load' directive, which is known for causing heavy contention\n"
" when used with threads. Please consider using 'lua-load-per-thread'\n"
" instead if your code is safe to run in parallel on multiple threads.\n");
DISGUISE(write(2, trash.area, trash.data));
}
else if (get_tainted() & TAINTED_LUA_STUCK) {
chunk_printf(&trash,
"### Note: at least one thread was stuck in a Lua context in a way that suggests\n"
" heavy processing inside a dependency or a long loop that can't yield.\n"
" Please make sure any external code you may rely on is safe for use in\n"
" an event-driven engine.\n");
DISGUISE(write(2, trash.area, trash.data));
}
#endif
for (;;)
abort();
}