122 lines
3.8 KiB
Diff
122 lines
3.8 KiB
Diff
From 3cdc9b2959f34e30fd99222ec0df0ecde4fa42cf Mon Sep 17 00:00:00 2001
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From: David Hildenbrand <dahi@linux.vnet.ibm.com>
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Date: Mon, 11 May 2015 17:52:06 +0200
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Subject: [PATCH 01/14] uaccess: count pagefault_disable() levels in
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pagefault_disabled
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.0/patches-4.0.4-rt1.tar.xz
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Until now, pagefault_disable()/pagefault_enabled() used the preempt
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count to track whether in an environment with pagefaults disabled (can
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be queried via in_atomic()).
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This patch introduces a separate counter in task_struct to count the
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level of pagefault_disable() calls. We'll keep manipulating the preempt
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count to retain compatibility to existing pagefault handlers.
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It is now possible to verify whether in a pagefault_disable() envionment
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by calling pagefault_disabled(). In contrast to in_atomic() it will not
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be influenced by preempt_enable()/preempt_disable().
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This patch is based on a patch from Ingo Molnar.
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Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
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---
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include/linux/sched.h | 1 +
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include/linux/uaccess.h | 36 +++++++++++++++++++++++++++++-------
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kernel/fork.c | 3 +++
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3 files changed, 33 insertions(+), 7 deletions(-)
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--- a/include/linux/sched.h
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+++ b/include/linux/sched.h
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@@ -1718,6 +1718,7 @@ struct task_struct {
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#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
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unsigned long task_state_change;
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#endif
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+ int pagefault_disabled;
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};
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/* Future-safe accessor for struct task_struct's cpus_allowed. */
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--- a/include/linux/uaccess.h
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+++ b/include/linux/uaccess.h
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@@ -2,20 +2,36 @@
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#define __LINUX_UACCESS_H__
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#include <linux/preempt.h>
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+#include <linux/sched.h>
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#include <asm/uaccess.h>
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+static __always_inline void pagefault_disabled_inc(void)
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+{
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+ current->pagefault_disabled++;
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+}
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+
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+static __always_inline void pagefault_disabled_dec(void)
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+{
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+ current->pagefault_disabled--;
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+ WARN_ON(current->pagefault_disabled < 0);
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+}
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+
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/*
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- * These routines enable/disable the pagefault handler in that
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- * it will not take any locks and go straight to the fixup table.
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+ * These routines enable/disable the pagefault handler. If disabled, it will
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+ * not take any locks and go straight to the fixup table.
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+ *
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+ * We increase the preempt and the pagefault count, to be able to distinguish
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+ * whether we run in simple atomic context or in a real pagefault_disable()
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+ * context.
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+ *
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+ * For now, after pagefault_disabled() has been called, we run in atomic
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+ * context. User access methods will not sleep.
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*
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- * They have great resemblance to the preempt_disable/enable calls
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- * and in fact they are identical; this is because currently there is
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- * no other way to make the pagefault handlers do this. So we do
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- * disable preemption but we don't necessarily care about that.
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*/
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static inline void pagefault_disable(void)
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{
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preempt_count_inc();
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+ pagefault_disabled_inc();
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/*
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* make sure to have issued the store before a pagefault
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* can hit.
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@@ -25,18 +41,24 @@ static inline void pagefault_disable(voi
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static inline void pagefault_enable(void)
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{
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-#ifndef CONFIG_PREEMPT
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/*
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* make sure to issue those last loads/stores before enabling
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* the pagefault handler again.
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*/
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barrier();
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+ pagefault_disabled_dec();
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+#ifndef CONFIG_PREEMPT
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preempt_count_dec();
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#else
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preempt_enable();
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#endif
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}
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+/*
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+ * Is the pagefault handler disabled? If so, user access methods will not sleep.
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+ */
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+#define pagefault_disabled() (current->pagefault_disabled != 0)
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+
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#ifndef ARCH_HAS_NOCACHE_UACCESS
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static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
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--- a/kernel/fork.c
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+++ b/kernel/fork.c
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@@ -1350,6 +1350,9 @@ static struct task_struct *copy_process(
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p->hardirq_context = 0;
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p->softirq_context = 0;
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#endif
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+
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+ p->pagefault_disabled = 0;
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+
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#ifdef CONFIG_LOCKDEP
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p->lockdep_depth = 0; /* no locks held yet */
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p->curr_chain_key = 0;
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