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author | Oleg Nesterov <oleg@redhat.com> | 2014-09-02 19:57:23 +0200 |
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committer | H. Peter Anvin <hpa@linux.intel.com> | 2014-09-02 14:51:16 -0700 |
commit | f1853505d9ca1c3ea27c29cf83c24661531c527b (patch) | |
tree | 724f80f438400a192baba1ef9c28119475894ba8 /arch/x86 | |
parent | 31d963389f67165402aa447a8e8ce5ffb9188b3d (diff) | |
download | op-kernel-dev-f1853505d9ca1c3ea27c29cf83c24661531c527b.zip op-kernel-dev-f1853505d9ca1c3ea27c29cf83c24661531c527b.tar.gz |
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 'arch/x86')
-rw-r--r-- | arch/x86/kernel/process.c | 13 |
1 files changed, 6 insertions, 7 deletions
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index f804dc9..b9ba9d5 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -64,14 +64,13 @@ EXPORT_SYMBOL_GPL(task_xstate_cachep); */ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) { - int ret; - *dst = *src; - if (fpu_allocated(&src->thread.fpu)) { - memset(&dst->thread.fpu, 0, sizeof(dst->thread.fpu)); - ret = fpu_alloc(&dst->thread.fpu); - if (ret) - return ret; + + memset(&dst->thread.fpu, 0, sizeof(dst->thread.fpu)); + if (tsk_used_math(src)) { + int err = fpu_alloc(&dst->thread.fpu); + if (err) + return err; fpu_copy(dst, src); } return 0; |