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[PING][RFC][BZ #1874] Fix assertion triggered by thread/fork interaction
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: libc-alpha at sourceware dot org, libc-ports at sourceware dot org
- Date: Thu, 2 Jan 2014 21:30:29 +0100
- Subject: [PING][RFC][BZ #1874] Fix assertion triggered by thread/fork interaction
- Authentication-results: sourceware.org; auth=none
- References: <20131009200534 dot GA4300 at domone dot podge>
On Wed, Oct 09, 2013 at 10:05:34PM +0200, OndÅej BÃlka wrote:
> This bug had a simple patch for five years without reply.
> Could someone comment this?
> It was detected on custom chip, could this be replicated on other
> An analysis from bugzilla and patch are below
> If a thread happens to hold dl_load_lock and have r_state set to RT_ADD
> or RT_DELETE at the time another thread calls fork(), then the child exit
> code from fork (in nptl/sysdeps/unix/sysv/linux/fork.c in our case)
> re-initializes dl_load_lock but does not restore r_state to RT_CONSISTENT.
> If the child subsequently requires ld.so functionality before calling exec(),
> then the assertion will fire.
> The patch acquires dl_load_lock on entry to fork() and releases it on exit
> from the parent path. The child path is initialized as currently done.
> This is essentially pthreads_atfork, but forced to be first because the
> acquisition of dl_load_lock must happen before malloc_atfork is active
> to avoid a deadlock.
> --- glibc-2.5-sources/nptl/sysdeps/unix/sysv/linux/fork.c
> 2007-05-29 23:44:33.000000000 -0400
> +++ glibc-2.5-modified/nptl/sysdeps/unix/sysv/linux/fork.c
> 2007-05-31 15:07:18.712221827 -0400
> @@ -27,6 +27,7 @@
> #include "fork.h"
> #include <hp-timing.h>
> #include <ldsodefs.h>
> +#include <bits/libc-lock.h>
> #include <bits/stdio-lock.h>
> #include <atomic.h>
> @@ -59,6 +60,8 @@
> struct used_handler *next;
> } *allp = NULL;
> + /* grab ld.so lock BEFORE switching to malloc_atfork */
> + __rtld_lock_lock_recursive (GL(dl_load_lock));
> /* Run all the registered preparation handlers. In reverse order.
> While doing this we build up a list of all the entries. */
> struct fork_handler *runp;
> @@ -208,6 +211,8 @@
> allp = allp->next;
> + /* unlock ld.so last, because we locked it first */
> + __rtld_lock_unlock_recursive (GL(dl_load_lock));
> return pid;