linux-kernel - simd: Allow simd use in kernel threads with softirqs disabled

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Message-ID: <20141114154315.GA15771@gondor.apana.org.au>
Date:	Fri, 14 Nov 2014 23:43:15 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Steffen Klassert <steffen.klassert@...unet.com>,
	Ming Liu <ming.liu@...driver.com>
Subject: simd: Allow simd use in kernel threads with softirqs disabled

While working on the cryptd request reordering problem, I noticed
an anomaly where kernel threads are normally allowed to use simd
per may_use_simd, but as soon as you disable softirqs, they suddenly
lose that ability for no good reason.

The problem is that in_interrupt does not distinguish between
softirq processing and simply having softirqs disabled.  This
patch creates a new helper in_serving_interrupt which makes that
distinction.  It then uses this in all current implementations
of may_use_simd.

Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index a9a4229..6cdaa852 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -63,7 +63,7 @@ static inline bool interrupted_user_mode(void)
  */
 bool irq_fpu_usable(void)
 {
-	return !in_interrupt() ||
+	return !in_serving_interrupt() ||
 		interrupted_user_mode() ||
 		interrupted_kernel_fpu_idle();
 }
diff --git a/include/asm-generic/simd.h b/include/asm-generic/simd.h
index f57eb7b..74e0b05 100644
--- a/include/asm-generic/simd.h
+++ b/include/asm-generic/simd.h
@@ -10,5 +10,5 @@
  */
 static __must_check inline bool may_use_simd(void)
 {
-	return !in_interrupt();
+	return !in_serving_interrupt();
 }
diff --git a/include/linux/preempt_mask.h b/include/linux/preempt_mask.h
index dbeec4d..18f3b46 100644
--- a/include/linux/preempt_mask.h
+++ b/include/linux/preempt_mask.h
@@ -65,6 +65,8 @@
 #define in_softirq()		(softirq_count())
 #define in_interrupt()		(irq_count())
 #define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
+#define in_serving_interrupt()	(irq_count() & (HARDIRQ_MASK | \
+						SOFTIRQ_OFFSET | NMI_MASK))
 
 /*
  * Are we in NMI context?

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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