Re: [PATCH] Make math_state_restore() save and restore the interruptflag

From: Nate Eldredge
Date: Thu Feb 06 2014 - 00:26:34 EST

On Sun, 2 Feb 2014, Suresh Siddha wrote:

Here is the second patch, which should fix the issue reported in this
thread. Maarten, Nate, George, please give this patch a try as is and
see if it helps address the issue you ran into. And please ack/review
with your test results.

3.13 plus this patch: boots and fixes the testcase I reported (core dump on ecrypt).

Tested-by: Nate Eldredge <nate@xxxxxxxxxxxxxxxxxxxx>

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 4e5f770..670bba1 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -87,10 +87,19 @@ EXPORT_SYMBOL(__kernel_fpu_begin);

void __kernel_fpu_end(void)
- if (use_eager_fpu())
- math_state_restore();
- else
+ if (use_eager_fpu()) {
+ /*
+ * For eager fpu, most the time, tsk_used_math() is true.
+ * Restore the user math as we are done with the kernel usage.
+ * At few instances during thread exit, signal handling etc,
+ * tsk_used_math() is false. Those few places will take proper
+ * actions, so we don't need to restore the math here.
+ */
+ if (likely(tsk_used_math(current)))
+ math_state_restore();
+ } else {
+ }

Nate Eldredge

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