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

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>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 43 insertions, 9 deletions

diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index fa581192de21..07d67309451a 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 *regs, struct sigcontext __user *sc)
                  * 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 sigcontext __user *sc)
         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;
 }