Re: GFP_ATOMIC allocations...

[Doug Ledford <dledford@redhat.com>]

On Thu, Aug 29, 2002 at 11:47:55AM +0100, Alan Cox wrote:
> On Thu, 2002-08-29 at 02:42, Doug Ledford wrote:
> > > Do GFP_KERNEL alloc failures during boot time just return NULL?
> > 
> > GFP_ATOMIC returns NULL on failure, GFP_KERNEL *should* never fail until 
> > we get to a true OOM condition because it will block and wait for the vm 
> > subsystem to free us up some space.  Under true OOM conditions it will 
> > return NULL AFAIK.
> 
> Or maybe deadlock if its happening due to I/O.

That would be a trick indeed since Patrick and I were referring to the
scanning code so the device isn't even configured for kernel use yet :-P

> If it wants to flush a
> page out to that scsi device and the scsi device is doing the allocation
> life gets very unpleasant.

Of course.  This is why the mid layer doesn't typically allocate anything 
at all once initial setup of a device is complete.  No allocations once 
setup is complete means no deadlock.

> SCSI may not be coming from block layer
> access with PF_MEM* set either, think about /proc and scsi-generic
> 
> "Here be dragons"

That's why I recommended people think each use through instead of blindly 
changing things ;-)

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
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