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[PATCH] Retry {save,restore}_fp_context if failed in atomic context.

To: linux-mips@linux-mips.org
Subject: [PATCH] Retry {save,restore}_fp_context if failed in atomic context.
From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Date: Mon, 16 Apr 2007 23:19:44 +0900 (JST)
Cc: ralf@linux-mips.org
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
The save_fp_context()/restore_fp_context() might sleep on accessing
user stack and therefore might lose FPU ownership in middle of them.

If these function failed due to "in_atomic" test in do_page_fault,
touch the sigcontext area in non-atomic context and retry these
save/restore operation.

This is a replacement of a (broken) fix which was titled "Allow CpU
exception in kernel partially".

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
---
This patch depends on:
> Subject: Re: [PATCH] Disallow CpU exception in kernel again.
> Message-Id: <20070414.023726.128617751.anemo@mba.ocn.ne.jp>

 arch/mips/kernel/signal-common.h |    9 ++++++
 arch/mips/kernel/signal.c        |   52 +++++++++++++++++++++++++++++++------
 arch/mips/kernel/signal32.c      |   52 +++++++++++++++++++++++++++++++------
 include/asm-mips/fpu.h           |    9 +++++-
 4 files changed, 102 insertions(+), 20 deletions(-)

diff --git a/arch/mips/kernel/signal-common.h b/arch/mips/kernel/signal-common.h
index 297dfcb..c0faabd 100644
--- a/arch/mips/kernel/signal-common.h
+++ b/arch/mips/kernel/signal-common.h
@@ -34,4 +34,13 @@ extern int install_sigtramp(unsigned int
 /* Check and clear pending FPU exceptions in saved CSR */
 extern int fpcsr_pending(unsigned int __user *fpcsr);
 
+/* Make sure we will not lose FPU ownership */
+#ifdef CONFIG_PREEMPT
+#define lock_fpu_owner()       preempt_disable()
+#define unlock_fpu_owner()     preempt_enable()
+#else
+#define lock_fpu_owner()       pagefault_disable()
+#define unlock_fpu_owner()     pagefault_enable()
+#endif
+
 #endif /* __SIGNAL_COMMON_H */
diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index fa58119..07d6730 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -20,6 +20,7 @@
 #include <linux/ptrace.h>
 #include <linux/unistd.h>
 #include <linux/compiler.h>
+#include <linux/uaccess.h>
 
 #include <asm/abi.h>
 #include <asm/asm.h>
@@ -27,7 +28,6 @@
 #include <asm/cacheflush.h>
 #include <asm/fpu.h>
 #include <asm/sim.h>
-#include <asm/uaccess.h>
 #include <asm/ucontext.h>
 #include <asm/cpu-features.h>
 #include <asm/war.h>
@@ -78,6 +78,46 @@ struct rt_sigframe {
 /*
  * Helper routines
  */
+static int protected_save_fp_context(struct sigcontext __user *sc)
+{
+       int err;
+       while (1) {
+               lock_fpu_owner();
+               own_fpu_inatomic(1);
+               err = save_fp_context(sc); /* this might fail */
+               unlock_fpu_owner();
+               if (likely(!err))
+                       break;
+               /* touch the sigcontext and try again */
+               err = __put_user(0, &sc->sc_fpregs[0]) |
+                       __put_user(0, &sc->sc_fpregs[31]) |
+                       __put_user(0, &sc->sc_fpc_csr);
+               if (err)
+                       break;  /* really bad sigcontext */
+       }
+       return err;
+}
+
+static int protected_restore_fp_context(struct sigcontext __user *sc)
+{
+       int err, tmp;
+       while (1) {
+               lock_fpu_owner();
+               own_fpu_inatomic(0);
+               err = restore_fp_context(sc); /* this might fail */
+               unlock_fpu_owner();
+               if (likely(!err))
+                       break;
+               /* touch the sigcontext and try again */
+               err = __get_user(tmp, &sc->sc_fpregs[0]) |
+                       __get_user(tmp, &sc->sc_fpregs[31]) |
+                       __get_user(tmp, &sc->sc_fpc_csr);
+               if (err)
+                       break;  /* really bad sigcontext */
+       }
+       return err;
+}
+
 int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
 {
        int err = 0;
@@ -113,10 +153,7 @@ int setup_sigcontext(struct pt_regs *reg
                 * Save FPU state to signal context. Signal handler
                 * will "inherit" current FPU state.
                 */
-               preempt_disable();
-               own_fpu(1);
-               err |= save_fp_context(sc);
-               preempt_enable();
+               err |= protected_save_fp_context(sc);
        }
        return err;
 }
@@ -148,10 +185,7 @@ check_and_restore_fp_context(struct sigc
        err = sig = fpcsr_pending(&sc->sc_fpc_csr);
        if (err > 0)
                err = 0;
-       preempt_disable();
-       own_fpu(0);
-       err |= restore_fp_context(sc);
-       preempt_enable();
+       err |= protected_restore_fp_context(sc);
        return err ?: sig;
 }
 
diff --git a/arch/mips/kernel/signal32.c b/arch/mips/kernel/signal32.c
index 53a337c..b9a0144 100644
--- a/arch/mips/kernel/signal32.c
+++ b/arch/mips/kernel/signal32.c
@@ -22,6 +22,7 @@
 #include <linux/compat.h>
 #include <linux/suspend.h>
 #include <linux/compiler.h>
+#include <linux/uaccess.h>
 
 #include <asm/abi.h>
 #include <asm/asm.h>
@@ -29,7 +30,6 @@
 #include <linux/bitops.h>
 #include <asm/cacheflush.h>
 #include <asm/sim.h>
-#include <asm/uaccess.h>
 #include <asm/ucontext.h>
 #include <asm/system.h>
 #include <asm/fpu.h>
@@ -176,6 +176,46 @@ struct rt_sigframe32 {
 /*
  * sigcontext handlers
  */
+static int protected_save_fp_context32(struct sigcontext32 __user *sc)
+{
+       int err;
+       while (1) {
+               lock_fpu_owner();
+               own_fpu_inatomic(1);
+               err = save_fp_context32(sc); /* this might fail */
+               unlock_fpu_owner();
+               if (likely(!err))
+                       break;
+               /* touch the sigcontext and try again */
+               err = __put_user(0, &sc->sc_fpregs[0]) |
+                       __put_user(0, &sc->sc_fpregs[31]) |
+                       __put_user(0, &sc->sc_fpc_csr);
+               if (err)
+                       break;  /* really bad sigcontext */
+       }
+       return err;
+}
+
+static int protected_restore_fp_context32(struct sigcontext32 __user *sc)
+{
+       int err, tmp;
+       while (1) {
+               lock_fpu_owner();
+               own_fpu_inatomic(0);
+               err = restore_fp_context32(sc); /* this might fail */
+               unlock_fpu_owner();
+               if (likely(!err))
+                       break;
+               /* touch the sigcontext and try again */
+               err = __get_user(tmp, &sc->sc_fpregs[0]) |
+                       __get_user(tmp, &sc->sc_fpregs[31]) |
+                       __get_user(tmp, &sc->sc_fpc_csr);
+               if (err)
+                       break;  /* really bad sigcontext */
+       }
+       return err;
+}
+
 static int setup_sigcontext32(struct pt_regs *regs,
                              struct sigcontext32 __user *sc)
 {
@@ -209,10 +249,7 @@ static int setup_sigcontext32(struct pt_
                 * Save FPU state to signal context.  Signal handler
                 * will "inherit" current FPU state.
                 */
-               preempt_disable();
-               own_fpu(1);
-               err |= save_fp_context32(sc);
-               preempt_enable();
+               err |= protected_save_fp_context32(sc);
        }
        return err;
 }
@@ -225,10 +262,7 @@ check_and_restore_fp_context32(struct si
        err = sig = fpcsr_pending(&sc->sc_fpc_csr);
        if (err > 0)
                err = 0;
-       preempt_disable();
-       own_fpu(0);
-       err |= restore_fp_context32(sc);
-       preempt_enable();
+       err |= protected_restore_fp_context32(sc);
        return err ?: sig;
 }
 
diff --git a/include/asm-mips/fpu.h b/include/asm-mips/fpu.h
index 71436f9..b414a7d 100644
--- a/include/asm-mips/fpu.h
+++ b/include/asm-mips/fpu.h
@@ -100,14 +100,19 @@ static inline void __own_fpu(void)
        set_thread_flag(TIF_USEDFPU);
 }
 
-static inline void own_fpu(int restore)
+static inline void own_fpu_inatomic(int restore)
 {
-       preempt_disable();
        if (cpu_has_fpu && !__is_fpu_owner()) {
                __own_fpu();
                if (restore)
                        _restore_fp(current);
        }
+}
+
+static inline void own_fpu(int restore)
+{
+       preempt_disable();
+       own_fpu_inatomic(restore);
        preempt_enable();
 }
 

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