diff options
author | Oleg Nesterov <oleg@redhat.com> | 2014-09-02 13:57:23 -0400 |
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committer | H. Peter Anvin <hpa@linux.intel.com> | 2014-09-02 17:51:16 -0400 |
commit | f1853505d9ca1c3ea27c29cf83c24661531c527b (patch) | |
tree | 724f80f438400a192baba1ef9c28119475894ba8 /kernel/seccomp.c | |
parent | 31d963389f67165402aa447a8e8ce5ffb9188b3d (diff) |
x86, fpu: copy_process: Avoid fpu_alloc/copy if !used_math()
arch_dup_task_struct() copies thread.fpu if fpu_allocated(), this
looks suboptimal and misleading. Say, a forking process could use
FPU only once in a signal handler but now tsk_used_math(src) == F,
in this case the child gets a copy of fpu->state for no reason. The
child won't use the saved registers anyway even if it starts to use
FPU, this can only avoid fpu_alloc() in do_device_not_available().
Change this code to check tsk_used_math(current) instead. We still
need to clear fpu->has_fpu/state, we could do this memset(0) under
fpu_allocated() check but I think this doesn't make sense. See also
the next change.
use_eager_fpu() assumes that fpu_allocated() is always true, but a
forking task (and thus its child) must always have PF_USED_MATH set,
otherwise the child can either use FPU without used_math() (note that
switch_fpu_prepare() doesn't do stts() in this case), or it will be
killed by do_device_not_available()->BUG_ON(use_eager_fpu).
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20140902175723.GA21659@redhat.com
Reviewed-by: Suresh Siddha <sbsiddha@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'kernel/seccomp.c')
0 files changed, 0 insertions, 0 deletions