VProc child-sibling list race

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VProc child-sibling list race

by Roger Tsang :: Rate this Message:

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Hi,

This bug is either staring right at me or I am just having a bad hair day. In vpop_wait() we see VPROC LOCK is used to protect its parent-child-sibling list. However the ND LIST lock doesn't protect PVP(vo)->pvp_childl from other threads. Also if I am not wrong the for-loop in vpop_wait() is not SMP-safe since PVP(vc)->pvp_childl is neither protected by VPROC LOCK nor ND LIST lock.

-Roger

<snip>
VPROC_LOCK_EXCL(vp, "vpop_wait");
<snip>
        for (vo = NULL, vc = pvp->pvp_head_childl;
                                vc != NULL;
                                vo = vc, vc = PVP(vc)->pvp_childl) {
<snip>
                                VPROC_LOCK_ND_LIST_EXCL(vp, "vpop_wait");
                                if (vo == NULL)
                                        pvp->pvp_head_childl = pvc->pvp_childl;
                                else
                                        PVP(vo)->pvp_childl = pvc->pvp_childl;
                                rmb();
                                pvc->pvp_childl = NULL;
                                VPROC_UNLOCK_ND_LIST_EXCL(vp, "vpop_wait");
<snip>
VPROC_UNLOCK_EXCL(vp, "vpop_wait");

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Re: VProc child-sibling list race

by Roger Tsang :: Rate this Message:

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In the latest CVS there is a regression in switch_exec_pids() that would eventually cause an oops decrementing reference count on an already released vproc at vpop_wait() while running glibc tst-exec4 from ssic-linux-bugs-2000692. I checked in the fix.

On Wed, Nov 4, 2009 at 6:18 AM, Roger Tsang <roger.tsang@...> wrote:

Hi,

This bug is either staring right at me or I am just having a bad hair day. In vpop_wait() we see VPROC LOCK is used to protect its parent-child-sibling list. However the ND LIST lock doesn't protect PVP(vo)->pvp_childl from other threads. Also if I am not wrong the for-loop in vpop_wait() is not SMP-safe since PVP(vc)->pvp_childl is neither protected by VPROC LOCK nor ND LIST lock.

-Roger

<snip>
VPROC_LOCK_EXCL(vp, "vpop_wait");
<snip>
        for (vo = NULL, vc = pvp->pvp_head_childl;
                                vc != NULL;
                                vo = vc, vc = PVP(vc)->pvp_childl) {
<snip>
                                VPROC_LOCK_ND_LIST_EXCL(vp, "vpop_wait");
                                if (vo == NULL)
                                        pvp->pvp_head_childl = pvc->pvp_childl;
                                else
                                        PVP(vo)->pvp_childl = pvc->pvp_childl;
                                rmb();
                                pvc->pvp_childl = NULL;
                                VPROC_UNLOCK_ND_LIST_EXCL(vp, "vpop_wait");
<snip>
VPROC_UNLOCK_EXCL(vp, "vpop_wait");

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trial. Simplify your report design, integration and deployment - and focus on
what you do best, core application coding. Discover what's new with
Crystal Reports now. http://p.sf.net/sfu/bobj-july
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