On Wed, Jan 18, 2017 at 2:16 PM, David Smith <[email protected]> wrote: > On 01/16/2017 03:14 PM, Thomas Gleixner wrote: >> On Mon, 16 Jan 2017, David Smith wrote: >> >>> If you call access_ok() with page faulting disabled, you'll still see >>> this new warning. >> >> And how so? It's just checking for task context. page fault disable/enable >> has absolutely nothing to do with that. > > True, task context and page fault disable/enable have nothing to do with each > other. However, the access_ok() comment states: > > * Context: User context only. This function may sleep if pagefaults are > * enabled. > > That seems to indicate that the function won't sleep if pagefaults are > disabled, and thus there is no need for a CONFIG_DEBUG_ATOMIC_SLEEP warning > if pagefaults are disabled.
ISTM even with pagefault_disable() in play, using access_ok() from, say, interrupt context is dangerous unless you've first checked that you're in a task. But I guess that in_task() would still return false, e.g. in perf. > >>> If you put that new access_ok() call in a module that gets >>> loaded/unloaded, you see one warning for every module load, which gets a >>> bit annoying. >> >> Can you please elaborate where this access_ok() is placed in the module >> code? > > It doesn't really matter where you place the access_ok() call in the module > code. If you call access_ok() in a module, then that module has its own > WARN_ON_ONCE() static variable. If access_ok() was a function exported from > the kernel, then there would be only one copy of the WARN_ON_ONCE() static > variable. That doesn't seem like such a big deal to me.
