From: "Ondřej Bílka" <neleai@seznam.cz>
To: libc-alpha@sourceware.org, libc-ports@sourceware.org
Subject: [PING][RFC][BZ #1874] Fix assertion triggered by thread/fork interaction
Date: Thu, 02 Jan 2014 20:30:00 -0000 [thread overview]
Message-ID: <20140102203029.GF25179@domone> (raw)
In-Reply-To: <20131009200534.GA4300@domone.podge>
ping
On Wed, Oct 09, 2013 at 10:05:34PM +0200, OndÅej BÃlka wrote:
> Hi,
>
> This bug had a simple patch for five years without reply.
> https://sourceware.org/bugzilla/show_bug.cgi?id=4578
> Could someone comment this?
>
> It was detected on custom chip, could this be replicated on other
> architectures?
>
> An analysis from bugzilla and patch are below
>
> "
> Details:
>
> 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;
next prev parent reply other threads:[~2014-01-02 20:30 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-09 20:05 [RFC][BZ " Ondřej Bílka
2013-10-17 15:41 ` Ondřej Bílka
2014-01-02 20:30 ` Ondřej Bílka [this message]
2014-01-02 22:18 ` Mike Frysinger
2014-01-02 23:54 ` Ondřej Bílka
2014-01-03 2:07 ` Mike Frysinger
2014-01-11 12:07 ` Ondřej Bílka
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