Re: [Xen-devel] [PATCH v2] tools/xenstore: try to get minimum thread stack size for watch thread

[Jim Fehlig <jfehlig@xxxxxxxx>]

On 02/26/2018 01:46 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>
> ---
> V2:
> - use _GNU_SOURCE (Wei Liu)
> - call __pthread_get_minstack() with parameter
> - add -ldl to correct make flags
> - ensure to not using smaller stack size than today
> ---
>   tools/xenstore/Makefile |  4 ++++
>   tools/xenstore/xs.c     | 21 ++++++++++++++++++++-
>   2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/tools/xenstore/Makefile b/tools/xenstore/Makefile
> index 2b99d2bc1b..0831be0b6f 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
> +libxenstore.so.$(MAJOR).$(MINOR): LDFLAGS += -ldl
> +endif
Dropping this patch in one of my automated builds caused a libxenstore link 
failure

[   99s] gcc    -lsystemd -ldl -pthread -Wl,-soname -Wl,libxenstore.so.3.0 
-shared -o libxenstore.so.3.0.3 xs.opic xs_lib.opic 
/home/abuild/rpmbuild/BUILD/xen-4.10.0-testing/tools/xenstore/../../tools/libs/toolcore/libxentoolcore.so 

[   99s] 
/home/abuild/rpmbuild/BUILD/xen-4.10.0-testing/tools/xenstore/../../tools/xenstore/libxenstore.so: 
undefined reference to `dlsym'
I hacked around it by appending '-ldl' to the end of the subsequent 
libxenstore.so rule.
>   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..77700bff2b 100644
> --- a/tools/xenstore/xs.c
> +++ b/tools/xenstore/xs.c
> @@ -16,6 +16,8 @@
>       License along with this library; If not, see 
> <http://www.gnu.org/licenses/>.
>   */
>   
> +#define _GNU_SOURCE
> +
>   #include <sys/types.h>
>   #include <sys/stat.h>
>   #include <fcntl.h>
> @@ -47,6 +49,10 @@ struct xs_stored_msg {
>   
>   #include <pthread.h>
>   
> +#ifdef USE_DLSYM
> +#include <dlfcn.h>
> +#endif
> +
>   struct xs_handle {
>         /* Communications channel to xenstore daemon. */
>         int fd;
> @@ -810,12 +816,25 @@ 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)(pthread_attr_t *attr);
> +#endif
>   
>   		if (pthread_attr_init(&attr) != 0) {
>                         mutex_unlock(&h->request_mutex);
>                         return false;
>                 }
> -               if (pthread_attr_setstacksize(&attr, READ_THREAD_STACKSIZE) != 
> 0) {
> +               if (!stack_size) {
> +#ifdef USE_DLSYM
> +                       getsz = dlsym(RTLD_DEFAULT, "__pthread_get_minstack");
> +                       if (getsz)
> +                               stack_size = getsz(&attr);
> +#endif
> +                       if (stack_size < READ_THREAD_STACKSIZE)
> +                               stack_size = READ_THREAD_STACKSIZE;
> +               }
> +               if (pthread_attr_setstacksize(&attr, stack_size) != 0) {
>                         pthread_attr_destroy(&attr);
>                         mutex_unlock(&h->request_mutex);
>                         return false;
This worked fine, even on the system with the buggy glibc.

Tested-by: Jim Fehlig <jfehlig@xxxxxxxx>

Regards,
Jim

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