10 files changed, 180 insertions, 14 deletions

diff --git a/arch/um/include/kern_util.h b/arch/um/include/kern_util.h
index 50a49691e0e..8d7f7c1cb9c 100644
--- a/arch/um/include/kern_util.h
+++ b/arch/um/include/kern_util.h
@@ -117,4 +117,7 @@ extern void sigio_handler(int sig, union uml_pt_regs *regs);
 
 extern void copy_sc(union uml_pt_regs *regs, void *from);
 
+unsigned long to_irq_stack(int sig, unsigned long *mask_out);
+unsigned long from_irq_stack(int nested);
+
 #endif
diff --git a/arch/um/kernel/dyn.lds.S b/arch/um/kernel/dyn.lds.S
index e36f92b463c..87a4e4427d8 100644
--- a/arch/um/kernel/dyn.lds.S
+++ b/arch/um/kernel/dyn.lds.S
@@ -97,6 +97,8 @@ SECTIONS
   .data           : {
     . = ALIGN(KERNEL_STACK_SIZE);               /* init_task */
     *(.data.init_task)
+    . = ALIGN(KERNEL_STACK_SIZE);
+    *(.data.init_irqstack)
     *(.data .data.* .gnu.linkonce.d.*)
     SORT(CONSTRUCTORS)
   }
diff --git a/arch/um/kernel/init_task.c b/arch/um/kernel/init_task.c
index f5385a3799b..d4f1d1ab252 100644
--- a/arch/um/kernel/init_task.c
+++ b/arch/um/kernel/init_task.c
@@ -1,5 +1,5 @@
-/* 
- * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,intel.linux}.com)
  * Licensed under the GPL
  */
 
@@ -33,14 +33,18 @@ EXPORT_SYMBOL(init_task);
 /*
  * Initial thread structure.
  *
- * We need to make sure that this is 16384-byte aligned due to the
+ * We need to make sure that this is aligned due to the
  * way process stacks are handled. This is done by having a special
  * "init_task" linker map entry..
  */
 
-union thread_union init_thread_union 
-__attribute__((__section__(".data.init_task"))) = 
-{ INIT_THREAD_INFO(init_task) };
+union thread_union init_thread_union
+        __attribute__((__section__(".data.init_task"))) =
+                { INIT_THREAD_INFO(init_task) };
+
+union thread_union cpu0_irqstack
+        __attribute__((__section__(".data.init_irqstack"))) =
+                { INIT_THREAD_INFO(init_task) };
 
 void unprotect_stack(unsigned long stack)
 {
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
index a9651a175eb..dba04d88b43 100644
--- a/arch/um/kernel/irq.c
+++ b/arch/um/kernel/irq.c
@@ -32,6 +32,7 @@
 #include "sigio.h"
 #include "um_malloc.h"
 #include "misc_constants.h"
+#include "as-layout.h"
 
 /*
  * Generic, controller-independent functions:
@@ -468,3 +469,113 @@ int init_aio_irq(int irq, char *name, irq_handler_t handler)
  out:
         return err;
 }
+
+/*
+ * IRQ stack entry and exit:
+ *
+ * Unlike i386, UML doesn't receive IRQs on the normal kernel stack
+ * and switch over to the IRQ stack after some preparation.  We use
+ * sigaltstack to receive signals on a separate stack from the start.
+ * These two functions make sure the rest of the kernel won't be too
+ * upset by being on a different stack.  The IRQ stack has a
+ * thread_info structure at the bottom so that current et al continue
+ * to work.
+ *
+ * to_irq_stack copies the current task's thread_info to the IRQ stack
+ * thread_info and sets the tasks's stack to point to the IRQ stack.
+ *
+ * from_irq_stack copies the thread_info struct back (flags may have
+ * been modified) and resets the task's stack pointer.
+ *
+ * Tricky bits -
+ *
+ * What happens when two signals race each other?  UML doesn't block
+ * signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
+ * could arrive while a previous one is still setting up the
+ * thread_info.
+ *
+ * There are three cases -
+ *     The first interrupt on the stack - sets up the thread_info and
+ * handles the interrupt
+ *     A nested interrupt interrupting the copying of the thread_info -
+ * can't handle the interrupt, as the stack is in an unknown state
+ *     A nested interrupt not interrupting the copying of the
+ * thread_info - doesn't do any setup, just handles the interrupt
+ *
+ * The first job is to figure out whether we interrupted stack setup.
+ * This is done by xchging the signal mask with thread_info->pending.
+ * If the value that comes back is zero, then there is no setup in
+ * progress, and the interrupt can be handled.  If the value is
+ * non-zero, then there is stack setup in progress.  In order to have
+ * the interrupt handled, we leave our signal in the mask, and it will
+ * be handled by the upper handler after it has set up the stack.
+ *
+ * Next is to figure out whether we are the outer handler or a nested
+ * one.  As part of setting up the stack, thread_info->real_thread is
+ * set to non-NULL (and is reset to NULL on exit).  This is the
+ * nesting indicator.  If it is non-NULL, then the stack is already
+ * set up and the handler can run.
+ */
+
+static unsigned long pending_mask;
+
+unsigned long to_irq_stack(int sig, unsigned long *mask_out)
+{
+        struct thread_info *ti;
+        unsigned long mask, old;
+        int nested;
+
+        mask = xchg(&pending_mask, 1 << sig);
+        if(mask != 0){
+                /* If any interrupts come in at this point, we want to
+                 * make sure that their bits aren't lost by our
+                 * putting our bit in.  So, this loop accumulates bits
+                 * until xchg returns the same value that we put in.
+                 * When that happens, there were no new interrupts,
+                 * and pending_mask contains a bit for each interrupt
+                 * that came in.
+                 */
+                old = 1 << sig;
+                do {
+                        old |= mask;
+                        mask = xchg(&pending_mask, old);
+                } while(mask != old);
+                return 1;
+        }
+
+        ti = current_thread_info();
+        nested = (ti->real_thread != NULL);
+        if(!nested){
+                struct task_struct *task;
+                struct thread_info *tti;
+
+                task = cpu_tasks[ti->cpu].task;
+                tti = task_thread_info(task);
+                *ti = *tti;
+                ti->real_thread = tti;
+                task->stack = ti;
+        }
+
+        mask = xchg(&pending_mask, 0);
+        *mask_out |= mask | nested;
+        return 0;
+}
+
+unsigned long from_irq_stack(int nested)
+{
+        struct thread_info *ti, *to;
+        unsigned long mask;
+
+        ti = current_thread_info();
+
+        pending_mask = 1;
+
+        to = ti->real_thread;
+        current->stack = to;
+        ti->real_thread = NULL;
+        *to = *ti;
+
+        mask = xchg(&pending_mask, 0);
+        return mask & ~1;
+}
+
diff --git a/arch/um/kernel/skas/process.c b/arch/um/kernel/skas/process.c
index a96ae1a0610..2a69a7ce579 100644
--- a/arch/um/kernel/skas/process.c
+++ b/arch/um/kernel/skas/process.c
@@ -163,8 +163,12 @@ static int start_kernel_proc(void *unused)
 
 extern int userspace_pid[];
 
+extern char cpu0_irqstack[];
+
 int start_uml_skas(void)
 {
+        stack_protections((unsigned long) &cpu0_irqstack);
+        set_sigstack(cpu0_irqstack, THREAD_SIZE);
         if(proc_mm)
                 userspace_pid[0] = start_userspace(0);
 
diff --git a/arch/um/kernel/uml.lds.S b/arch/um/kernel/uml.lds.S
index f6301274cf3..bc59f97e34d 100644
--- a/arch/um/kernel/uml.lds.S
+++ b/arch/um/kernel/uml.lds.S
@@ -59,6 +59,8 @@ SECTIONS
   {
     . = ALIGN(KERNEL_STACK_SIZE);               /* init_task */
     *(.data.init_task)
+    . = ALIGN(KERNEL_STACK_SIZE);
+    *(.data.init_irqstack)
     *(.data)
     *(.gnu.linkonce.d*)
     CONSTRUCTORS
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 420ee86d0d1..18e5c8b67eb 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -117,6 +117,46 @@ void remove_sigstack(void)
 
 void (*handlers[_NSIG])(int sig, struct sigcontext *sc);
 
+void handle_signal(int sig, struct sigcontext *sc)
+{
+        unsigned long pending = 0;
+
+        do {
+                int nested, bail;
+
+                /*
+                 * pending comes back with one bit set for each
+                 * interrupt that arrived while setting up the stack,
+                 * plus a bit for this interrupt, plus the zero bit is
+                 * set if this is a nested interrupt.
+                 * If bail is true, then we interrupted another
+                 * handler setting up the stack.  In this case, we
+                 * have to return, and the upper handler will deal
+                 * with this interrupt.
+                 */
+                bail = to_irq_stack(sig, &pending);
+                if(bail)
+                        return;
+
+                nested = pending & 1;
+                pending &= ~1;
+
+                while((sig = ffs(pending)) != 0){
+                        sig--;
+                        pending &= ~(1 << sig);
+                        (*handlers[sig])(sig, sc);
+                }
+
+                /* Again, pending comes back with a mask of signals
+                 * that arrived while tearing down the stack.  If this
+                 * is non-zero, we just go back, set up the stack
+                 * again, and handle the new interrupts.
+                 */
+                if(!nested)
+                        pending = from_irq_stack(nested);
+        } while(pending);
+}
+
 extern void hard_handler(int sig);
 
 void set_handler(int sig, void (*handler)(int), int flags, ...)
diff --git a/arch/um/os-Linux/sys-i386/signal.c b/arch/um/os-Linux/sys-i386/signal.c
index 0d3eae51835..f311609f93d 100644
--- a/arch/um/os-Linux/sys-i386/signal.c
+++ b/arch/um/os-Linux/sys-i386/signal.c
@@ -1,15 +1,13 @@
 /*
- * Copyright (C) 2006 Jeff Dike (jdike@addtoit.com)
+ * Copyright (C) 2006 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Licensed under the GPL
  */
 
 #include <signal.h>
 
-extern void (*handlers[])(int sig, struct sigcontext *sc);
+extern void handle_signal(int sig, struct sigcontext *sc);
 
 void hard_handler(int sig)
 {
-        struct sigcontext *sc = (struct sigcontext *) (&sig + 1);
-
-        (*handlers[sig])(sig, sc);
+        handle_signal(sig, (struct sigcontext *) (&sig + 1));
 }
diff --git a/arch/um/os-Linux/sys-x86_64/signal.c b/arch/um/os-Linux/sys-x86_64/signal.c
index 3f369e5f976..82a388822cd 100644
--- a/arch/um/os-Linux/sys-x86_64/signal.c
+++ b/arch/um/os-Linux/sys-x86_64/signal.c
@@ -1,16 +1,16 @@
 /*
- * Copyright (C) 2006 Jeff Dike (jdike@addtoit.com)
+ * Copyright (C) 2006 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Licensed under the GPL
  */
 
 #include <signal.h>
 
-extern void (*handlers[])(int sig, struct sigcontext *sc);
+extern void handle_signal(int sig, struct sigcontext *sc);
 
 void hard_handler(int sig)
 {
         struct ucontext *uc;
         asm("movq %%rdx, %0" : "=r" (uc));
 
-        (*handlers[sig])(sig, (struct sigcontext *) &uc->uc_mcontext);
+        handle_signal(sig, (struct sigcontext *) &uc->uc_mcontext);
 }
diff --git a/include/asm-um/thread_info.h b/include/asm-um/thread_info.h
index 261e2f4528f..18a13ba7460 100644
--- a/include/asm-um/thread_info.h
+++ b/include/asm-um/thread_info.h
@@ -22,6 +22,7 @@ struct thread_info {
                                                    0-0xBFFFFFFF for user
                                                    0-0xFFFFFFFF for kernel */
         struct restart_block    restart_block;
+        struct thread_info      *real_thread;    /* Points to non-IRQ stack */
 };
 
 #define INIT_THREAD_INFO(tsk)                   \
@@ -35,6 +36,7 @@ struct thread_info {
         .restart_block =  {                     \
                 .fn =  do_no_restart_syscall,   \
         },                                      \
+        .real_thread = NULL,                    \
 }
 
 #define init_thread_info        (init_thread_union.thread_info)