(In reply to Filip Krska from comment #0)
> Description of problem:
> 
> zsh deadlocks in futex-wait state when signal hit in malloc() called by
> lexsave():
> 
> 
> #0  __lll_lock_wait_private () at
> ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:97
> 97	2:	movl	%edx, %eax
> (gdb) bt
> #0  __lll_lock_wait_private () at
> ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:97
> #1  0x0000003eb427d0a0 in _L_lock_5189 () from /lib64/libc-2.12.so
> #2  0x0000003eb42789fb in _int_free (av=0x3eb458fe80, p=0x2174940,
> have_lock=0) at malloc.c:4959
> ...
> #7  0x0000000000474495 in zhandler (sig=17) at signals.c:584
> #8  <signal handler called>
> #9  _int_malloc (av=0x3eb458fe80, bytes=<value optimized out>) at
> malloc.c:4538
> #10 0x0000003eb427a991 in __libc_malloc (bytes=264) at malloc.c:3664
> #11 0x000000000044a96b in lexsave () at lex.c:252

I agree that replacing malloc() by zalloc() will prevent the above backtrace.

> Recheck of any possible malloc() signal leaks in current RHEL 6 zsh code
> needed.

It is unfortunately not that easy.  Calling [z]free() can also cause such a deadlock.  Upstream discouraged from wrapping [z]free() by signal queuing globally because it could hide unprotected accesses to the global state and result in wrong behavior (which is actually worse than the deadlock).

The handling of signals is still not perfect even in the latest upstream version of zsh.  See bug #1198671 for the list of related upstream fixes.  Unfortunately, new bug reports are still coming on the upstream mailing list.

(In reply to Filip Krska from comment #0)
> Recheck of any possible malloc() signal leaks in current RHEL 6 zsh code
> needed.

I have found one more occurrence (still present in the latest upstream):

--- a/Src/mem.c
+++ b/Src/mem.c
@@ -1289,18 +1289,23 @@ zsfree(char *p)
 MALLOC_RET_T
 realloc(MALLOC_RET_T p, MALLOC_ARG_T size)
 {
     struct m_hdr *m = (struct m_hdr *)(((char *)p) - M_ISIZE), *mp, *mt;
     char *r;
     int i, l = 0;

     /* some system..., see above */
-    if (!p && size)
-       return (MALLOC_RET_T) malloc(size);
+    if (!p && size) {
+       queue_signals();
+       r = malloc(size);
+       unqueue_signals();
+       return (MALLOC_RET_T) r;
+    }
+
     /* and some systems even do this... */
     if (!p || !size)
        return (MALLOC_RET_T) p;

     queue_signals();  /* just queue signals caught rather than handling them */

     /* check if we are reallocating a small block, if we do, we have
        to compute the size of the block from the sort of block it is in */

Created attachment 1084827 [details]
proposed fix

Filip. could you please review the attached patch?

Comment on attachment 1084827 [details]
proposed fix

Good catch IMHO, I'd add that chunk as well. Thanks

(In reply to Kamil Dudka from comment #6)
> I have found one more occurrence (still present in the latest upstream):

Sent upstream:

http://www.zsh.org/mla/workers/2015/msg02822.html

The fix for this bug has been delivered in RHEL 6.7.z and this component has not been updated in RHEL 6.8. RHEL 6.8 contains the fix from RHEL 6.7.z. Therefore, this bug has been closed as CURRENTRELEASE.