restarting SYSCALL system call on amd64 loses arguments

[Konstantin Belousov]

On Tue, Sep 24, 2013 at 09:19:49PM +0200, Jilles Tjoelker wrote:
> On Tue, Sep 24, 2013 at 12:37:30AM +0300, Konstantin Belousov wrote:
> > On Mon, Sep 23, 2013 at 10:26:13PM +0200, Tijl Coosemans wrote:
> > > Has anyone taken a look at this PR yet?
> 
> > > http://www.freebsd.org/cgi/query-pr.cgi?pr=182161
> 
> > This looks like a valid bug, but probably not a valid testcase.
> 
> > Let me elaborate.  When a signal is delivered, return from the signal
> > handler is performed by the sigreturn(2), which reloads the whole
> > register file when crossing kernel->user boundary due to sys_sigreturn(9)
> > setting PCB_FULL_IRET flag.  As result, the whole trap frame at the
> > time of the syscall entry is restored, and ERESTART return is not
> > exercised.
> 
> > I was not able to reproduce the issue with the supplied test program
> > on HEAD.  I suspect that the program actually exposed the bug in the
> > signal delivery in the threaded processes, which I introduced for 9.1
> > and fixed in r251047 & r251365.
> 
> The ERESTART return happens if there is no signal or no longer a signal.
> The latter is how the bug in the PR occurs: a SIGCHLD delivery via
> handler in one thread races with a SIGCHLD acceptance in wait4() in
> another thread. Note wait4() returning a value in the other thread in
> the fourth line of the kdump output in the PR.
> 
> For some reason, I can reproduce this easily on my local quad-core
> r255729 stable/9 system but not on ref9-amd64.freebsd.org or
> ref10-amd64.freebsd.org.
> 
> I can also reproduce the bug on my local system by racing signal
> delivery via handler with acceptance in sigtimedwait().

So, could you, please, check the r255844 on your machine ?
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