lkml.org 
[lkml]   [2010]   [Apr]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [stable] [PATCH 2.6.29.x - 2.6.31.1] module: fix __module_ref_addr()
On Mon, Mar 29, 2010 at 10:22:38PM -0400, Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@goodmis.org) wrote:
> > On Mon, 2010-03-29 at 14:07 -0700, Greg KH wrote:
> > > On Mon, Mar 29, 2010 at 04:09:46PM -0400, Mathieu Desnoyers wrote:
> > > > * Steven Rostedt (rostedt@goodmis.org) wrote:
> > > > > This patch does not apply to 2.6.34-rc, and the code in upstream looks
> > > > > to have been fixed. Should this go to stable?
> > > >
> > > > Yes. 2.6.34-rc does not have this issue anymore, but the patch is needed in
> > > > -stable.
> > >
> > > Why is this not in .34-rc2? Can you find the specific patch in Linus's
> > > tree that solves this and let stable@kernel.org know about it?
> > >
> >
> > Looks like it was this commit:
> >
> > commit e1783a240f491fb233f04edc042e16b18a7a79ba
> > Author: Christoph Lameter <cl@linux-foundation.org>
> > Date: Tue Jan 5 15:34:50 2010 +0900
> > module: Use this_cpu_xx to dynamically allocate counters
> >
> > Mathieu's fix was:
> >
> > - return (local_t *) (mod->refptr + per_cpu_offset(cpu));
> > + return (local_t *) per_cpu_ptr(mod->refptr, cpu);
> >
> > As Mathieu states in his change log, the bug is that the mod->refptr is
> > outside the assembly obfuscation of the per_cpu_offset(). This allows
> > the compiler to optimize and cause a NULL pointer dereference with the
> > manipulation of per cpu data.
> >
> > Christoph Lameter's change fixes this bug as a side effect:
> >
> > -static inline local_t *__module_ref_addr(struct module *mod, int cpu)
> > -{
> > -#ifdef CONFIG_SMP
> > - return (local_t *) (mod->refptr + per_cpu_offset(cpu));
> > -#else
> > - return &mod->ref;
> > -#endif
> > -}
> > -
> > /* Sometimes we know we already have a refcount, and it's easier not
> > to handle the error case (which only happens with rmmod --wait). */
> > static inline void __module_get(struct module *module)
> > {
> > if (module) {
> > - unsigned int cpu = get_cpu();
> > - local_inc(__module_ref_addr(module, cpu));
> > + preempt_disable();
> > + __this_cpu_inc(module->refptr->count);
> > trace_module_get(module, _THIS_IP_,
> > - local_read(__module_ref_addr(module, cpu)));
> > - put_cpu();
> > + __this_cpu_read(module->refptr->count));
> > + preempt_enable();
> > }
> > }
> >
> > By removing the buggy code all together.
>
> Exactly. Steven has beaten me on the start line on this one. ;)

Ok, I'm totally confused now :(

What patch should I apply to a stable release, and which stable release?

thanks,

greg k-h


\
 
 \ /
  Last update: 2010-04-19 20:35    [W:0.678 / U:0.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site