RE: [PATCH 01/12] usbnet: introduce usbnet 3 command helpers

On Wed, Oct 10, 2012 at 6:08 PM, Oliver Neukum [off-list ref] wrote:

quoted

A reset always applies to the whole device. Resets are used in error
handling of block devices (storage and uas). If you reset a device,
pre_reset() and post_reset() of all interfaces need to be called. So they
are part of the SCSI error handler. SCSI error handlers can allocate memory
only with GFP_NOIO (or GFP_ATOMIC) because any IO for paging
can cause the SCSI layer to wait for the error handling to finish. The error
handling can only finish when pre/post_reset() have finished. Catch-22

IMO, it is not practical to obey the rule for drivers, because driver may
call many other kernel component API which may allocate memory
via GFP_KERNEL in the path easily.

What about the error handler/sleep/resume code calling into the
memory allocator to indicate that all allocates be GFP_NOIO until
it calls back to indicate that the restricted path is complete.
Might be a per-cpu count?

	David



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On Wed, Oct 10, 2012 at 7:25 PM, David Laight [off-list ref] wrote:

What about the error handler/sleep/resume code calling into the
memory allocator to indicate that all allocates be GFP_NOIO until
it calls back to indicate that the restricted path is complete.
Might be a per-cpu count?

IMO, it might be a per-task variable, but unfortunately no such
mechanism is provided by current kernel.

Thanks,
--
Ming Lei