On Mon, 18 Apr 2011, Dave Hansen wrote:
> > > +void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...)
> > > +{
> > > + va_list args;
> > > + unsigned int filter = SHOW_MEM_FILTER_NODES;
> > > + const gfp_t wait = gfp_mask & __GFP_WAIT;
> > > +
> >
> > "wait" is unnecessary. You didn't do "const gfp_t nowarn = gfp_mask &
> > __GFP_NOWARN;" for the same reason.
>
> This line is just a copy from the __alloc_pages_slowpath() one. I guess
> we only use it once, so I've got no problem killing it.
>
> > > + if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs))
> > > + return;
> > > +
> > > + /*
> > > + * This documents exceptions given to allocations in certain
> > > + * contexts that are allowed to allocate outside current's set
> > > + * of allowed nodes.
> > > + */
> > > + if (!(gfp_mask & __GFP_NOMEMALLOC))
> > > + if (test_thread_flag(TIF_MEMDIE) ||
> > > + (current->flags & (PF_MEMALLOC | PF_EXITING)))
> > > + filter &= ~SHOW_MEM_FILTER_NODES;
> > > + if (in_interrupt() || !wait)
> > > + filter &= ~SHOW_MEM_FILTER_NODES;
> > > +
> > > + if (fmt) {
> > > + printk(KERN_WARNING);
> > > + va_start(args, fmt);
> > > + vprintk(fmt, args);
> > > + va_end(args);
> > > + }
> > > +
> > > + printk(KERN_WARNING "%s: page allocation failure: order:%d, mode:0x%x\n",
> > > + current->comm, order, gfp_mask);
> >
> > pr_warning()?
>
> OK, I'll change it back.
>
> > current->comm should always be printed with get_task_comm() to avoid
> > racing with /proc/pid/comm. Since this function can be called potentially
> > deep in the stack, you may need to serialize this with a
> > statically-allocated buffer.
>
> This code was already in page_alloc.c. I'm simply breaking it out here
> trying to keep the changes down to what is needed minimally to move the
> code. Correcting this preexisting problem sounds like a great follow-on
> patch.
>
It shouldn't be a follow-on patch since you're introducing a new feature
here (vmalloc allocation failure warnings) and what I'm identifying is a
race in the access to current->comm. A bug fix for a race should always
preceed a feature that touches the same code.
There's two options to fixing the race:
- provide a statically-allocated buffer to use for get_task_comm() and
copy current->comm over before printing it, or
- take task_lock(current) to protect against /proc/pid/comm.
The latter probably isn't safe because we could potentially already be
holding task_lock(current) during a GFP_ATOMIC page allocation.
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