Re: Fixed PR13146 by not allowing memory allocations to sleep (Was: [SCM] systemtap: system-wide probe/trace tool branch, master, updated. release-1.6-151-g8e794e9)

[Jim Keniston <jkenisto at linux dot vnet dot ibm dot com>]

On Tue, 2011-09-27 at 15:03 -0700, Josh Stone wrote:
> On 09/27/2011 07:52 AM, Mark Wielaard wrote:
> > Hi David,
> > 
> > On Thu, 2011-09-01 at 14:39 +0000, dsmith@sourceware.org wrote:
> >> commit 8e794e9dfeea5a48b84442b92dea6c17b9ef75d1
> >> Author: David Smith <dsmith@redhat.com>
> >> Date:   Thu Sep 1 09:39:15 2011 -0500
> >>
> >>     Fixed PR13146 by not allowing memory allocations to sleep.
> >>     
> >>     * runtime/alloc.c:  Turn off __GFP_WAIT when allocating memory.
> >>     * runtime/transport/ring_buffer.c (__stp_alloc_ring_buffer): Ditto.
> >>     * runtime/counter.c (_stp_counter_init): Handles memory allocation failure
> >>       better.
> >>     * runtime/task_finder.c (__stp_call_mmap_callbacks_with_addr): Better
> >>       cleanup if memory allocation fails.
> > 
> > Sorry for the late reply. But I am suspecting this commit of causing
> > accasional (though not very frequent) test failures that say:
> >   ERROR: context (size 8352) allocation failed
> > 
> > I suspect that is caused because the context is one of the larger
> > allocations at systemtap_module_init time. And because we are no longer
> > allowed to GFP_WAIT it is more likely to fail now. Would it be
> > possible/make sense to allow GFP_WAIT for allocations made from context
> > like systemtap_module_init() that may sleep because they are made from
> > user context?
> 
> I agree, those contexts which can sleep, should.  Not only does this
> make it more likely we'll get the memory we want, but also makes us
> better citizens with the rest of the kernel.
> 
> Josh
> 

I haven't seen this explicitly mentioned wrt this thread or PR13146, but
uprobes and uretprobe handlers (which are called from the utrace
report_signal callback) can sleep.

Jim