On Sun, Sep 15, 2024 at 12:23:31PM +0200, Linus Torvalds wrote: > On Sun, 15 Sept 2024 at 12:08, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote: > > > > The lru_add_drain() function at the start of zap_page_range_single() takes a > > mutex. > > Yes, that shouldn't be problematic. But: > > > It's the preempt_disable() in gru_fault() which is the issue. The call tree > > is: > > > > gru_fault() <- disables preempt > > -> remap_pfn_range() > > -> remap_pfn_range_notrack() > > That code is very odd. It was invalid to call remap_pfn_range() with > preemption disabled even before, because it will allocate the page > tables that it fills in. > > But presumably *that* never happened in practice, and so nobody > noticed how broken that code was before. > > Now smatch seems to see a new problem, but I *think* it's because > smatch didn't notice the sleeping by p4d_alloc() / pud_alloc() / > pmd_alloc() because those allocations are all conditional (so smatch > doesn't see them as static violations). > > Put another way: I do not believe this is a new issue, but perhaps a > "new to smatch" issue? > Yep. You're right. Smatch doesn't count allocations as sleeping when we pass a variable to for the gfp flags and those functions do "get_zeroed_page(gfp)". I've been intending for years to handle bitmasks better but I've never implemented that code. regards, dan carpenter
