From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Fenghua Yu <fenghua.yu@intel.com>,
Suresh Siddha <sbsiddha@gmail.com>,
Bean Anderson <bean@azulsystems.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH 1/4] x86, fpu: introduce per-cpu "bool in_kernel_fpu"
Date: Fri, 29 Aug 2014 20:16:03 +0200 [thread overview]
Message-ID: <20140829181603.GB30659@redhat.com> (raw)
In-Reply-To: <20140829181533.GA30659@redhat.com>
interrupted_kernel_fpu_idle() tries to detect if kernel_fpu_begin()
is safe or not. In particulat it should obviously deny the nested
kernel_fpu_begin() and this logic doesn't look clean.
If use_eager_fpu() == T we rely on a) __thread_has_fpu() check in
interrupted_kernel_fpu_idle(), and b) on the fact that _begin() does
__thread_clear_has_fpu().
Otherwise we demand that the interrupted task has no FPU if it is in
kernel mode, this works becase __kernel_fpu_begin() does clts().
Add the per-cpu "bool in_kernel_fpu" variable, and change this code
to check/set/clear it. This allows to do some cleanups (see the next
changes) and fixes.
Note that the current code looks racy. Say, kernel_fpu_begin() right
after math_state_restore()->__thread_fpu_begin() will overwrite the
regs we are going to restore. This patch doesn't even try to fix this,
it just adds the comment, but "in_kernel_fpu" can also be used to
implement kernel_fpu_disable() / kernel_fpu_enable().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
arch/x86/include/asm/i387.h | 2 +-
arch/x86/kernel/i387.c | 10 ++++++++++
2 files changed, 11 insertions(+), 1 deletions(-)
diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index ed8089d..5e275d3 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -40,8 +40,8 @@ extern void __kernel_fpu_end(void);
static inline void kernel_fpu_begin(void)
{
- WARN_ON_ONCE(!irq_fpu_usable());
preempt_disable();
+ WARN_ON_ONCE(!irq_fpu_usable());
__kernel_fpu_begin();
}
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index d5dd808..8fb8868 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -19,6 +19,8 @@
#include <asm/fpu-internal.h>
#include <asm/user.h>
+static DEFINE_PER_CPU(bool, in_kernel_fpu);
+
/*
* Were we in an interrupt that interrupted kernel mode?
*
@@ -33,6 +35,9 @@
*/
static inline bool interrupted_kernel_fpu_idle(void)
{
+ if (this_cpu_read(in_kernel_fpu))
+ return false;
+
if (use_eager_fpu())
return __thread_has_fpu(current);
@@ -73,6 +78,9 @@ void __kernel_fpu_begin(void)
{
struct task_struct *me = current;
+ this_cpu_write(in_kernel_fpu, true);
+
+ /* FIXME: race with math_state_restore()-like code */
if (__thread_has_fpu(me)) {
__thread_clear_has_fpu(me);
__save_init_fpu(me);
@@ -99,6 +107,8 @@ void __kernel_fpu_end(void)
} else {
stts();
}
+
+ this_cpu_write(in_kernel_fpu, false);
}
EXPORT_SYMBOL(__kernel_fpu_end);
--
1.5.5.1
next prev parent reply other threads:[~2014-08-29 18:18 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-27 18:51 [PATCH 0/4] x86, fpu: copy_process's FPU paths cleanups Oleg Nesterov
2014-08-27 18:51 ` [PATCH 1/4] x86, fpu: change __thread_fpu_begin() to use use_eager_fpu() Oleg Nesterov
2014-08-27 18:51 ` [PATCH 2/4] x86, fpu: copy_process: avoid fpu_alloc/copy if !used_math() Oleg Nesterov
2014-08-27 18:52 ` [PATCH 3/4] x86, fpu: copy_process: sanitize fpu->last_cpu initialization Oleg Nesterov
2014-08-27 18:52 ` [PATCH 4/4] x86, fpu: shift "fpu_counter = 0" from copy_thread() to arch_dup_task_struct() Oleg Nesterov
2014-08-27 20:43 ` [PATCH 0/4] x86, fpu: copy_process's FPU paths cleanups H. Peter Anvin
2014-08-28 6:50 ` Ingo Molnar
2014-08-28 12:25 ` Oleg Nesterov
2014-08-28 10:38 ` Oleg Nesterov
2014-08-28 1:17 ` Linus Torvalds
2014-08-28 11:16 ` Oleg Nesterov
2014-08-29 18:15 ` [PATCH 0/4] x86, fpu: kernel_fpu_begin/end cleanups Oleg Nesterov
2014-08-29 18:16 ` Oleg Nesterov [this message]
2014-09-02 6:43 ` [PATCH 1/4] x86, fpu: introduce per-cpu "bool in_kernel_fpu" Suresh Siddha
2014-08-29 18:16 ` [PATCH 2/4] x86, fpu: don't abuse ->has_fpu in __kernel_fpu_begin/end Oleg Nesterov
2014-08-29 18:17 ` [PATCH 3/4] x86, fpu: irq_fpu_usable: always return true if use_eager_fpu() Oleg Nesterov
2014-08-29 18:17 ` [PATCH 4/4] x86, fpu: irq_fpu_usable: kill all checks except !in_kernel_fpu Oleg Nesterov
2014-09-02 7:04 ` Suresh Siddha
2014-09-02 12:58 ` Oleg Nesterov
2014-09-02 14:13 ` Oleg Nesterov
2014-09-02 5:04 ` [PATCH 0/4] x86, fpu: copy_process's FPU paths cleanups Suresh Siddha
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