x86/fpu: __kernel_fpu_begin() should clear fpu_owner_task even if use_eager_fpu()
authorOleg Nesterov <oleg@redhat.com>
Mon, 19 Jan 2015 18:51:32 +0000 (19:51 +0100)
committerBorislav Petkov <bp@suse.de>
Mon, 23 Feb 2015 14:50:28 +0000 (15:50 +0100)
commit7aeccb83e76316b365e4b44a1dd982ee22a7d8b2
tree9d17e8a0f9c68f33d36154da30e014c489a9f478
parentf353e612304ba752d6b613dc02eae8116cd3e27b
x86/fpu: __kernel_fpu_begin() should clear fpu_owner_task even if use_eager_fpu()

__kernel_fpu_begin() does nothing if !__thread_has_fpu() && use_eager_fpu(),
perhaps it assumes that this case is simply impossible. This is certainly
not possible if in_interrupt() == T; interrupted_user_mode() should have
FPU, and interrupted_kernel_fpu_idle() should fail if !__thread_has_fpu().

However, even if use_eager_fpu() == T a task can do drop_fpu(), then switch
to another thread which becomes fpu_owner_task, then resume and call some
function which does kernel_fpu_begin(). Say, an exiting task does a lot of
things after exit_thread(), it is not safe to assume that it can't use FPU
in these paths.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Suresh Siddha <sbsiddha@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Pekka Riikonen <priikone@iki.fi>
Link: http://lkml.kernel.org/r/20150119185132.GB16427@redhat.com
Signed-off-by: Borislav Petkov <bp@suse.de>
arch/x86/kernel/i387.c