On Mon, Aug 31, 2015 at 01:22:26PM +0800, yalin wang wrote: > why not provide API like: > fput() > fput_nosync() ? > > because synchronous version are reasonable and safe in most time, > let the user to select which version to use is more feasible, no matter if it > is kthread or not.
Synchronous version is *NOT* safe in a lot of situations, from "deep enough in kernel stack" to "now a function seven levels out in call chain happens to hold a mutex grabbed elsewhere inside a mutex taken by unexpected ->release() instance, causing a deadlock", etc. It's not sync vs. async; we still guarantee execution before return from syscall. The only case when we really get async is kernel threads - there we do *not* return to userland at all, so we have to schedule it really asynchronous. Which is why we need an explicit sync version (for kernel threads only, not exported, don't use unless you really understand what you are doing and can explain why that particular case is safe, etc.) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
