Re: [Xen-devel] [PATCH] xenstore: increase default thread stack size to 32k

[Juergen Gross <jgross@xxxxxxxx>]

On 21/02/18 23:13, Jim Fehlig wrote:
> On several Skylake machines I've observed xl segfaults when running
> create or destroy subcommands. Other subcommands may segfault too,
> but I've only looked at create and destroy which share a similar
> backtrace
> 
> Thread 2 (Thread 0x7ffff7ff3700 (LWP 2941)):
>     at /usr/include/bits/unistd.h:44
>     at xs.c:398
>     fd=<optimized out>) at xs.c:1231
> 
> Thread 1 has canceled Thread 2 and is waiting for it in pthread_join().
> 
> The backtrace smelled of memory/stack overflow, which was verified by
> increasing DEFAULT_THREAD_STACKSIZE to 32kb. Presumably the stack
> overflow is observed on Skylake due to a broader CPU feature set which
> must be saved within _dl_runtime_resolve and friends.
> 
> While PTHREAD_STACK_MIN should advertise a suitable stack size based on
> the underlying system, increasing the default size makes xenstore a bit
> more robust on systems with insufficient/broken minimums.

We hit something like this before:

https://lists.xen.org/archives/html/xen-devel/2016-07/msg01727.html

The main problem is that any thread local storage is taken from the
stack without any interface being available for adjusting the _real_
stack size instead of the meory for thread local storage + stack.

So we can increase the stack size of the xenstore thread and wait for
the next breakage, or we have to think about a proper solution.

Right now I have no sensible idea how to address the problem, as the
old thread suggests the underlying glibc problem isn't fixed yet (wow:
the problem is known for more than 7 years now):

https://sourceware.org/bugzilla/show_bug.cgi?id=11787


Juergen

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