On Wed, Mar 29, 2006 at 10:26:29PM -0800, Andrew Morton wrote:
> Balbir Singh <[email protected]> wrote:
> >
> > > The kmem_cache_free() can happen outside the lock.
> >
> >
> > kmem_cache_free() and setting to NULL outside the lock is prone to
> > race conditions. Consider the following scenario
> >
> > A thread group T1 has exiting processes P1 and P2
> >
> > P1 is exiting, finishes the delay accounting by calling taskstats_exit_pid()
> > and gives up the mutex and calls kmem_cache_free(), but before it can set
> > tsk->delays to NULL, we try to get statistics for the entire thread group.
> > This task will show up in the thread group with a dangling tsk->delays.
>
> Yes, the `tsk->delays = NULL;' needs to happen inside the lock. But the
> kmem_cache_free() does not. It pointlessly increases the lock hold time.
Understood will fix it
>
> > > > + if (info->attrs[TASKSTATS_CMD_ATTR_PID]) {
> > > > + u32 pid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_PID]);
> > > > + rc = fill_pid((pid_t)pid, NULL, &stats);
> > >
> > > We shouldn't have a typecast here. If it generates a warning then we need
> > > to get in there and find out why.
> >
> > The reason for a typecast is that pid is passed as a u32 from userspace.
> > genetlink currently supports most unsigned types with little or no
> > support for signed types. We exchange data as u32 and do the correct
> > thing in the kernel. Would you like us to move away from this?
> >
>
> I think it's best to avoid the cast unless it's actually needed to avoid a
> warning or compile error, or to do special things with sign extension.
> Because casts clutter up the code and can hide real bugs. In this case the
> compiler should silently perform the conversion.
Yep, the compiler was doing it for me, but I tried to be smart and cast
things around. Will fix it.
Thanks,
Balbir
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