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 doesn't look clean.
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 some cleanups and fixes. Note that the current code looks racy. Say, kernel_fpu_begin() right after math_state_restore()->__thread_fpu_begin() will overwrite the regs we are going to restore. This patch doesn't try to fix this, it only adds a comment, but "in_kernel_fpu" can also be used to implement kernel_fpu_disable() / kernel_fpu_enable(). 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 <o...@redhat.com> --- arch/x86/include/asm/i387.h | 2 +- arch/x86/kernel/i387.c | 10 ++++++++++ 2 files changed, 11 insertions(+), 1 deletions(-) diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h index ed8089d..5e275d3 100644 --- a/arch/x86/include/asm/i387.h +++ b/arch/x86/include/asm/i387.h @@ -40,8 +40,8 @@ extern void __kernel_fpu_end(void); static inline void kernel_fpu_begin(void) { - WARN_ON_ONCE(!irq_fpu_usable()); preempt_disable(); + WARN_ON_ONCE(!irq_fpu_usable()); __kernel_fpu_begin(); } diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index d5dd808..8fb8868 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -19,6 +19,8 @@ #include <asm/fpu-internal.h> #include <asm/user.h> +static DEFINE_PER_CPU(bool, in_kernel_fpu); + /* * Were we in an interrupt that interrupted kernel mode? * @@ -33,6 +35,9 @@ */ static inline bool interrupted_kernel_fpu_idle(void) { + if (this_cpu_read(in_kernel_fpu)) + return false; + if (use_eager_fpu()) return __thread_has_fpu(current); @@ -73,6 +78,9 @@ void __kernel_fpu_begin(void) { struct task_struct *me = current; + this_cpu_write(in_kernel_fpu, true); + + /* FIXME: race with math_state_restore()-like code */ if (__thread_has_fpu(me)) { __thread_clear_has_fpu(me); __save_init_fpu(me); @@ -99,6 +107,8 @@ void __kernel_fpu_end(void) } else { stts(); } + + this_cpu_write(in_kernel_fpu, false); } EXPORT_SYMBOL(__kernel_fpu_end); -- 1.5.5.1 -- 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/