Re: [PATCH][BZ 21672] fix pthread_create crash in ia64

[Sergei Trofimovich <slyfox at gentoo dot org>]

On Wed, 2 Aug 2017 17:59:57 -0300
Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote:

> On 02/08/2017 17:53, Sergei Trofimovich wrote:
> > On Wed, 5 Jul 2017 22:47:17 +0100
> > Sergei Trofimovich <slyfox@gentoo.org> wrote:
> >   
> >> On Sun, 25 Jun 2017 23:07:15 +0100
> >> Sergei Trofimovich <slyfox@gentoo.org> wrote:
> >>  
> >>> Minimal reproducer:
> >>>
> >>>     #include <pthread.h>
> >>>
> >>>     static void * f (void * p) { return NULL; }
> >>>
> >>>     int main (int argc, const char ** argv) {
> >>>         pthread_t t;
> >>>         pthread_create (&t, NULL, &f, NULL);
> >>>
> >>>         pthread_join (t, NULL);
> >>>         return 0;
> >>>     }
> >>>
> >>>     $ gcc -O0 -ggdb3 -o r bug.c -pthread && ./r
> >>>
> >>>     Program terminated with signal SIGSEGV, Segmentation fault.
> >>>     #0  0x2000000000077da0 in start_thread (arg=0x0) at pthread_create.c:432
> >>>     432         __madvise (pd->stackblock, freesize - PTHREAD_STACK_MIN, MADV_DONTNEED);
> >>>
> >>> Here crash happens right after attempt to free unused part of
> >>> thread's stack.
> >>>
> >>> On most architectures stack grows only down or grows only up.
> >>> And there glibc decides which of unused ends of stack blocks can be freed.
> >>>
> >>> ia64 maintans two stacks. Both of them grow from the opposite directions:
> >>>  - normal "sp" stack (stack for local variables) grows down
> >>>  - register stack "bsp" grows up from the opposite end of stack block
> >>>
> >>> In this failure case we have prematurely freed "rsp" stack.
> >>>
> >>> The change leaves a few pages from both sides of stack block.
> >>>
> >>> Bug: https://sourceware.org/PR21672
> >>> Bug: https://bugs.gentoo.org/622694
> >>> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> >>> ---
> >>>  nptl/pthread_create.c | 18 ++++++++++++++++--
> >>>  1 file changed, 16 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
> >>> index 7a970ffc5b..6e3f6db5b1 100644
> >>> --- a/nptl/pthread_create.c
> >>> +++ b/nptl/pthread_create.c
> >>> @@ -555,10 +555,24 @@ START_THREAD_DEFN
> >>>    size_t pagesize_m1 = __getpagesize () - 1;
> >>>  #ifdef _STACK_GROWS_DOWN
> >>>    char *sp = CURRENT_STACK_FRAME;
> >>> -  size_t freesize = (sp - (char *) pd->stackblock) & ~pagesize_m1;
> >>> +  char *freeblock = (char *) pd->stackblock;
> >>> +  size_t freesize = (sp - freeblock) & ~pagesize_m1;
> >>>    assert (freesize < pd->stackblock_size);
> >>> +# ifdef __ia64__
> >>>    if (freesize > PTHREAD_STACK_MIN)
> >>> -    __madvise (pd->stackblock, freesize - PTHREAD_STACK_MIN, MADV_DONTNEED);
> >>> +    {
> >>> +      /* On ia64 stack grows both ways!
> >>> +         - normal "sp" stack (stack for local variables) grows down
> >>> +         - register stack "bsp" grows up from the opposite end of stack block
> >>> +
> >>> +         Thus we leave PTHREAD_STACK_MIN bytes from stack block top
> >>> +         and leave same PTHREAD_STACK_MIN at stack block bottom.  */
> >>> +      freeblock += PTHREAD_STACK_MIN;
> >>> +      freesize -= PTHREAD_STACK_MIN;
> >>> +    }
> >>> +# endif
> >>> +  if (freesize > PTHREAD_STACK_MIN)
> >>> +    __madvise (freeblock, freesize - PTHREAD_STACK_MIN, MADV_DONTNEED);
> >>>  #else
> >>>    /* Page aligned start of memory to free (higher than or equal
> >>>       to current sp plus the minimum stack size).  */
> >>> -- 
> >>> 2.13.1
> >>>     
> >>
> >> Ping :)  
> > 
> > Ping^2
> >   
> 
> What about https://sourceware.org/ml/libc-alpha/2017-07/msg00302.html ?

Oh, I didn't get that email back in my inbox. Fetching from UI.
Will testboth in SKI and real machine and report back in that thread.

[preliminary] Fix looks good to me.

Thank you!

-- 

  Sergei

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