On Tue, Apr 12, 2022 at 09:32:25PM +0800, Yanjun Zhu wrote: > 在 2022/4/12 0:02, Jason Gunthorpe 写道: > > On Mon, Apr 11, 2022 at 03:52:23PM +0000, Pearson, Robert B wrote: > > > > > > > Yes, you cannot use irq_save variants here. You have to know your calling context is non-atomic already and use the irq wrapper. > > > > > > Not sure why. If you call irqsave in a non-atomic context doesn't it > > > behave the same as irq? I.e. flags = 0. xarray provides > > > xa_lock_xxx() for people to use. Are you saying I have to call > > > xa_alloc_cyclic_xxx() instead which is the same thing? > > > > The xa_lock is a magic thing, when you call a __xa_*(.., GFP_KERNEL) > > type function then it will unlock and relock the xa_lock internally. > > > > Thus you cannot wrapper an irqsave lock across the GFP_KERNEL call > > sites because XA doesn't know the 'flags' to be able to properly > > unlock it. > > > > > The problem is I've gotten gun shy about people calling into the > > > verbs APIs in strange contexts. The rules don't seem to be written > > > down. If I could be certain that no one ever is allowed to call a > > > verbs API in an interrupt then this is correct but how do I know > > > that? > > > > rxe used GFP_KERNEL so it already has assumed it is a process context. > Got it. > > __xa_alloc_cyclic(..., GFP_NOWAIT) will unlock xa lock internally. But it > does not handle flags. So the irq is still disabled. Because GFP_NOWAIT is > used in __xa_alloc_cyclic, it will not sleep. > > __xa_alloc_cyclic will lock xa lock and return to xa_unlock_irqrestore. > > So the following code should be OK? > > xa_lock_irqsave(&pool->xa, flags); > err = __xa_alloc_cyclic(&pool->xa, &elem->index, elem, pool->limit, > &pool->next, GFP_NOWAIT); > xa_unlock_irqrestore(&pool->xa, flags); No, use GFP_KERNEL an use the proper irq or bh version of xa_alloc_cyclic. save is only required if you don't know the contex you are in, and here we know we are in a process context. Jason
