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. Ira diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index a0143dd24430..4cc50b554a29 100644 --- a/include/linux/workqueue.h +++ b/include/linux/workqueue.h @@ -199,7 +199,7 @@ struct execute_work { struct delayed_work n = __DELAYED_WORK_INITIALIZER(n, f, TIMER_DEFERRABLE) #ifdef CONFIG_DEBUG_OBJECTS_WORK -extern void __init_work(struct work_struct *work, int onstack); +extern void __init_work(struct work_struct *work); extern void destroy_work_on_stack(struct work_struct *work); extern void destroy_delayed_work_on_stack(struct delayed_work *work); static inline unsigned int work_static(struct work_struct *work) @@ -207,7 +207,7 @@ static inline unsigned int work_static(struct work_struct *work) return *work_data_bits(work) & WORK_STRUCT_STATIC; } #else -static inline void __init_work(struct work_struct *work, int onstack) { } +static inline void __init_work(struct work_struct *work) { } static inline void destroy_work_on_stack(struct work_struct *work) { } static inline void destroy_delayed_work_on_stack(struct delayed_work *work) { } static inline unsigned int work_static(struct work_struct *work) { return 0; } @@ -221,20 +221,20 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; } * to generate better code. */ #ifdef CONFIG_LOCKDEP -#define __INIT_WORK(_work, _func, _onstack) \ +#define __INIT_WORK(_work, _func) \ do { \ static struct lock_class_key __key; \ \ - __init_work((_work), _onstack); \ + __init_work(_work); \ (_work)->data = (atomic_long_t) WORK_DATA_INIT(); \ lockdep_init_map(&(_work)->lockdep_map, "(work_completion)"#_work, &__key, 0); \ INIT_LIST_HEAD(&(_work)->entry); \ (_work)->func = (_func); \ } while (0) #else -#define __INIT_WORK(_work, _func, _onstack) \ +#define __INIT_WORK(_work, _func) \ do { \ - __init_work((_work), _onstack); \ + __init_work(_work); \ (_work)->data = (atomic_long_t) WORK_DATA_INIT(); \ INIT_LIST_HEAD(&(_work)->entry); \ (_work)->func = (_func); \ @@ -242,10 +242,10 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; } #endif #define INIT_WORK(_work, _func) \ - __INIT_WORK((_work), (_func), 0) + __INIT_WORK((_work), (_func)) #define INIT_WORK_ONSTACK(_work, _func) \ - __INIT_WORK((_work), (_func), 1) + __INIT_WORK((_work), (_func)) #define __INIT_DELAYED_WORK(_work, _func, _tflags) \ do { \ diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 7cd5f5e7e0a1..7d87300cfbc6 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -515,9 +515,9 @@ static inline void debug_work_deactivate(struct work_struct *work) debug_object_deactivate(work, &work_debug_descr); } -void __init_work(struct work_struct *work, int onstack) +void __init_work(struct work_struct *work) { - if (onstack) + if (object_is_on_stack(work)) debug_object_init_on_stack(work, &work_debug_descr); else debug_object_init(work, &work_debug_descr);
