Re: [Xen-devel] [PATCH] tools/xenstore: try to get minimum thread stack size for watch thread

[Jim Fehlig <jfehlig@xxxxxxxx>]

On 02/22/2018 06:53 AM, Juergen Gross wrote:
> When creating a pthread in xs_watch() try to get the minimal needed
> size of the thread from glibc instead of using a constant. This avoids
> problems when the library is used in programs with large per-thread
> memory.
>
> Use dlsym() to get the pointer to __pthread_get_minstack() in order to
> avoid linkage problems and fall back to the current constant size if
> not found.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> Only compile tested. Jim, can you please verify this patch is solving
> your original problem?
It didn't help, but it could be due to my buggy glibc

# gdb xl
...
(gdb) r create test-hvm.xl
Starting program: /usr/sbin/xl create test-hvm.xl
Parsing config from test-hvm.xl
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff72d51c2 in __pthread_get_minstack () from /lib64/libpthread.so.0
(gdb) thr a a bt

Thread 1 (Thread 0x7ffff7fd8780 (LWP 2568)):
#0  0x00007ffff72d51c2 in __pthread_get_minstack () from /lib64/libpthread.so.0
#1  0x00007ffff66ae259 in xs_watch (h=0x55555578fc90,
    path=path@entry=0x555555798fa0 "/local/domain/0/device-model/2/state",
    token=token@entry=0x5555557990b0 "3/0") at xs.c:826
#2  0x00007ffff79476f4 in libxl__ev_xswatch_register 
(gc=gc@entry=0x5555557955f0,
    w=w@entry=0x555555797468, func=func@entry=0x7ffff793dd10 
<xswait_xswatch_callback>,
    path=0x555555798fa0 "/local/domain/0/device-model/2/state") at 
libxl_event.c:638
#3  0x00007ffff793deb0 in libxl__xswait_start (gc=gc@entry=0x5555557955f0,
    xswa=xswa@entry=0x5555557973e0) at libxl_aoutils.c:53
#4  0x00007ffff79326b0 in libxl__spawn_spawn (egc=egc@entry=0x7fffffffd950,
    ss=ss@entry=0x555555797370) at libxl_exec.c:292
#5  0x00007ffff79258d3 in libxl__spawn_local_dm (egc=0x7fffffffd950, 
dmss=<optimized out>)
    at libxl_dm.c:2400
#6  0x00007ffff791d3a7 in domcreate_launch_dm (egc=0x7fffffffd950, 
multidev=0x555555798168,
    ret=<optimized out>) at libxl_create.c:1379
#7  0x00007ffff7967275 in libxl__bootloader_run (egc=egc@entry=0x7fffffffd950,
    bl=bl@entry=0x555555796cc0) at libxl_bootloader.c:403
#8  0x00007ffff791ffe3 in initiate_domain_create (egc=egc@entry=0x7fffffffd950,
    dcs=dcs@entry=0x555555796610) at libxl_create.c:997
#9  0x00007ffff79201a1 in do_domain_create (ctx=ctx@entry=0x55555578f2a0,
    d_config=d_config@entry=0x7fffffffdb70, domid=domid@entry=0x7fffffffdaa8,
    restore_fd=restore_fd@entry=-1, send_back_fd=send_back_fd@entry=-1, 
params=params@entry=0x0,
    ao_how=0x0, aop_console_how=0x0) at libxl_create.c:1682
#10 0x00007ffff79204b6 in libxl_domain_create_new (ctx=0x55555578f2a0,
    d_config=d_config@entry=0x7fffffffdb70, domid=domid@entry=0x7fffffffdaa8,
    ao_how=ao_how@entry=0x0, aop_console_how=aop_console_how@entry=0x0) at 
libxl_create.c:1885
#11 0x00005555555780b4 in create_domain (dom_info=dom_info@entry=0x7fffffffe0b0)
    at xl_vmcontrol.c:902
#12 0x00005555555790c4 in main_create (argc=1, argv=0x7fffffffe378) at 
xl_vmcontrol.c:1207
#13 0x0000555555560c5b in main (argc=2, argv=0x7fffffffe370) at xl.c:384

If you like, I can try a patched glibc after the weekend :-).

Regards,
Jim

> ---
>   tools/xenstore/Makefile |  4 ++++
>   tools/xenstore/xs.c     | 19 ++++++++++++++++++-
>   2 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/tools/xenstore/Makefile b/tools/xenstore/Makefile
> index 2b99d2bc1b..fb6c73e297 100644
> --- a/tools/xenstore/Makefile
> +++ b/tools/xenstore/Makefile
> @@ -100,6 +100,10 @@ libxenstore.so.$(MAJOR): libxenstore.so.$(MAJOR).$(MINOR)
>         ln -sf $< $@
>   
>   xs.opic: CFLAGS += -DUSE_PTHREAD
> +ifeq ($(CONFIG_Linux),y)
> +xs.opic: CFLAGS += -DUSE_DLSYM
> +xs.opic: LDFLAGS += -ldl
> +endif
>   
>   libxenstore.so.$(MAJOR).$(MINOR): xs.opic xs_lib.opic
>         $(CC) $(LDFLAGS) $(PTHREAD_LDFLAGS) -Wl,$(SONAME_LDFLAG) 
> -Wl,libxenstore.so.$(MAJOR) $(SHLIB_LDFLAGS) -o $@ $^ $(LDLIBS_libxentoolcore) 
> $(SOCKET_LIBS) $(PTHREAD_LIBS) $(APPEND_LDFLAGS)
> diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
> index abffd9cd80..8372f5b1a4 100644
> --- a/tools/xenstore/xs.c
> +++ b/tools/xenstore/xs.c
> @@ -47,6 +47,11 @@ struct xs_stored_msg {
>   
>   #include <pthread.h>
>   
> +#ifdef USE_DLSYM
> +#define __USE_GNU
> +#include <dlfcn.h>
> +#endif
> +
>   struct xs_handle {
>         /* Communications channel to xenstore daemon. */
>         int fd;
> @@ -810,12 +815,24 @@ bool xs_watch(struct xs_handle *h, const char *path, 
> const char *token)
>         if (!h->read_thr_exists) {
>                 sigset_t set, old_set;
>                 pthread_attr_t attr;
> +               static size_t stack_size;
> +#ifdef USE_DLSYM
> +               size_t (*getsz)(void);
> +#endif
>   
> +		if (!stack_size) {
> +#ifdef USE_DLSYM
> +                       getsz = dlsym(RTLD_DEFAULT, "__pthread_get_minstack");
> +                       stack_size = getsz ? getsz() : READ_THREAD_STACKSIZE;
> +#else
> +                       stack_size = READ_THREAD_STACKSIZE;
> +#endif
> +               }
>                 if (pthread_attr_init(&attr) != 0) {
>                         mutex_unlock(&h->request_mutex);
>                         return false;
>                 }
> -               if (pthread_attr_setstacksize(&attr, READ_THREAD_STACKSIZE) != 
> 0) {
> +               if (pthread_attr_setstacksize(&attr, stack_size) != 0) {
>                         pthread_attr_destroy(&attr);
>                         mutex_unlock(&h->request_mutex);
>                         return false;

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