From 14e153ef75eecae8fd0738ffb42120f4962a00cd Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 15 Jan 2015 20:19:43 +0100 Subject: [PATCH] x86, fpu: Introduce per-cpu in_kernel_fpu state interrupted_kernel_fpu_idle() tries to detect if kernel_fpu_begin() is safe or not. In particular it should obviously deny the nested kernel_fpu_begin() and this logic looks very confusing. If use_eager_fpu() == T we rely on a) __thread_has_fpu() check in interrupted_kernel_fpu_idle(), and b) on the fact that _begin() does __thread_clear_has_fpu(). Otherwise we demand that the interrupted task has no FPU if it is in kernel mode, this works because __kernel_fpu_begin() does clts() and interrupted_kernel_fpu_idle() checks X86_CR0_TS. Add the per-cpu "bool in_kernel_fpu" variable, and change this code to check/set/clear it. This allows to do more cleanups and fixes, see the next changes. The patch also moves WARN_ON_ONCE() under preempt_disable() just to make this_cpu_read() look better, this is not really needed. And in fact I think we should move it into __kernel_fpu_begin(). Signed-off-by: Oleg Nesterov Reviewed-by: Rik van Riel Cc: matt.fleming@intel.com Cc: bp@suse.de Cc: pbonzini@redhat.com Cc: luto@amacapital.net Cc: Linus Torvalds Cc: Suresh Siddha Link: http://lkml.kernel.org/r/20150115191943.GB27332@redhat.com Signed-off-by: Thomas Gleixner --- Reading git-format-patch failed