Ira Weiny wrote: > On Wed, Nov 16, 2022 at 12:20:37PM -0600, Bjorn Helgaas wrote: > > On Wed, Nov 16, 2022 at 11:09:39AM +0100, Lukas Wunner wrote: > > > On Mon, Nov 14, 2022 at 05:19:43PM -0800, ira.weiny@xxxxxxxxx wrote: > > > > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > > > > > > > The callers of pci_doe_submit_task() allocate the pci_doe_task on the > > > > stack. This causes the work structure to be allocated on the stack > > > > without pci_doe_submit_task() knowing. Work item initialization needs > > > > to be done with either INIT_WORK_ONSTACK() or INIT_WORK() depending on > > > > how the work item is allocated. > > > > > > > > Jonathan suggested creating doe task allocation macros such as > > > > DECLARE_CDAT_DOE_TASK_ONSTACK().[1] The issue with this is the work > > > > function is not known to the callers and must be initialized correctly. > > > > > > > > A follow up suggestion was to have an internal 'pci_doe_work' item > > > > allocated by pci_doe_submit_task().[2] This requires an allocation which > > > > could restrict the context where tasks are used. > > > > > > > > Compromise with an intermediate step to initialize the task struct with > > > > a new call pci_doe_init_task() which must be called prior to submit > > > > task. > > > > > > > > [1] https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@xxxxxxxxxx/T/#m88a7f50dcce52f30c8bf5c3dcc06fa9843b54a2d > > > > [2] https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@xxxxxxxxxx/T/#m63c636c5135f304480370924f4d03c00357be667 > > > > > > We have object_is_on_stack(), included from <linux/sched/task_stack.h>. > > > > > > So you could just autosense in pci_doe_submit_task() whether > > > pci_doe_task is on the stack and call the appropriate INIT_WORK > > > variant. > > > > Nifty, I had no idea object_is_on_stack() existed, thank you! > > Indeed! Neither did I! thanks! > > > > > I wonder if there's an opportunity to use object_is_on_stack() > > somewhere in the INIT_WORK() path to find usage mistakes. > > I'm thinking we could make INIT_WORK do the right thing all the time. Not sure > what the overhead of object_is_on_stack() is. > > > > > Adding it in pci_doe_submit_task() would add some complexity, so I'm > > not sure whether it's worth adding it unless we actually have uses for > > both cases. > > I think if we don't do something we have to document that > pci_doe_submit_task() only works with tasks on the stack. > > I would rather just make pci_doe_submit_task() correct and not complicate the > callers. object_is_on_stack() can't be enough overhead to be worried about in > this call path can it? > > Actually after writing all that I wonder if we can't push the use of > object_is_on_stack() into the debug code? Something like below (completely > untested)? I think this could be pushed even further down but I'd like to get > opinions before attempting a change which will have a wider blast radius. This looks reasonable, but I would do it after and independently of introducing the autosensing version of pci_doe_submit_task(). Then you can pursue this line of thinking and come back to simplify pci_doe_submit_task() if it indeed moves forward.
