https://bugzilla.wikimedia.org/show_bug.cgi?id=67348

Tim Starling <[email protected]> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #5 from Tim Starling <[email protected]> ---
(In reply to Ori Livneh from comment #4)
> The crash I am able to easily reproduce is this:
> 
> # 0  bt_handler at /srv/hhvm-dev/hphp/util/process.h:81
> # 1  lua_sethook at /usr/lib/x86_64-linux-gnu/liblua5.1.so.0:0
> # 2  luasandbox_timer_handle_profiler at /srv/luasandbox/timer.c:218
> # 3  timer_sigev_thread at
> /build/buildd/eglibc-2.19/rt/../nptl/sysdeps/unix/sysv/linux/timer_routines.
> c:66
> # 4  start_thread at /build/buildd/eglibc-2.19/nptl/pthread_create.c:312
> # 5  clone at
> /build/buildd/eglibc-2.19/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:113
> 
> No PHP stack trace is present.

IIRC that was one of the issues fixed by
<https://github.com/facebook/hhvm/pull/3120>. The LuaSandbox object was
destroyed before the timer event was delivered, so dereferencing the user data
failed.

> Some cursory Googling produced a few posts in which people grumble about
> lua_sethook not being signal-safe, contrary to what is claimed in the
> source: http://lua-users.org/lists/lua-l/2012-02/msg00060.html

Theoretically, pointer reads and writes may be non-atomic, like far pointers in
[[real mode]], but they are atomic on x86-64.

The only remaining issue in LuaSandbox against my HHVM dev branch that I know
about is the fact that emergency timeouts don't work -- that will be fixed by
disabling them. I have tested a patch for this.

Anyway, the luasandbox_unprotect_recursion() issue was fixed, so any other
crash can go in a new bug report.

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