arch/tile: fix up some issues in calling do_work_pending()

First, we were at risk of handling thread-info flags, in particular
do_signal(), when returning from kernel space.  This could happen
after a failed kernel_execve(), or when forking a kernel thread.
The fix is to test in do_work_pending() for user_mode() and return
immediately if so; we already had this test for one of the flags,
so I just hoisted it to the top of the function.

Second, if a ptraced process updated the callee-saved registers
in the ptregs struct and then processed another thread-info flag, we
would overwrite the modifications with the original callee-saved
registers.  To fix this, we add a register to note if we've already
saved the registers once, and skip doing it on additional passes
through the loop.  To avoid a performance hit from the couple of
extra instructions involved, I modified the GET_THREAD_INFO() macro
to be guaranteed to be one instruction, then bundled it with adjacent
instructions, yielding an overall net savings.

Reported-By: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

4 files changed, 68 insertions, 27 deletions

diff --git a/arch/tile/include/asm/thread_info.h b/arch/tile/include/asm/thread_info.h
index bc4f562bd459..7594764d8a69 100644
--- a/arch/tile/include/asm/thread_info.h
+++ b/arch/tile/include/asm/thread_info.h
@@ -100,9 +100,14 @@ extern void cpu_idle_on_new_stack(struct thread_info *old_ti,
 
 #else /* __ASSEMBLY__ */
 
-/* how to get the thread information struct from ASM */
+/*
+ * How to get the thread information struct from assembly.
+ * Note that we use different macros since different architectures
+ * have different semantics in their "mm" instruction and we would
+ * like to guarantee that the macro expands to exactly one instruction.
+ */
 #ifdef __tilegx__
-#define GET_THREAD_INFO(reg) move reg, sp; mm reg, zero, LOG2_THREAD_SIZE, 63
+#define EXTRACT_THREAD_INFO(reg) mm reg, zero, LOG2_THREAD_SIZE, 63
 #else
 #define GET_THREAD_INFO(reg) mm reg, sp, zero, LOG2_THREAD_SIZE, 31
 #endif
diff --git a/arch/tile/kernel/intvec_32.S b/arch/tile/kernel/intvec_32.S
index 5d56a1ef5ba5..6943515100f8 100644
--- a/arch/tile/kernel/intvec_32.S
+++ b/arch/tile/kernel/intvec_32.S
@@ -839,6 +839,18 @@ STD_ENTRY(interrupt_return)
         FEEDBACK_REENTER(interrupt_return)
 
         /*
+         * Use r33 to hold whether we have already loaded the callee-saves
+         * into ptregs.  We don't want to do it twice in this loop, since
+         * then we'd clobber whatever changes are made by ptrace, etc.
+         * Get base of stack in r32.
+         */
+        {
+         GET_THREAD_INFO(r32)
+         movei  r33, 0
+        }
+
+.Lretry_work_pending:
+        /*
          * Disable interrupts so as to make sure we don't
          * miss an interrupt that sets any of the thread flags (like
          * need_resched or sigpending) between sampling and the iret.
@@ -848,9 +860,6 @@ STD_ENTRY(interrupt_return)
         IRQ_DISABLE(r20, r21)
         TRACE_IRQS_OFF  /* Note: clobbers registers r0-r29 */
 
-        /* Get base of stack in r32; note r30/31 are used as arguments here. */
-        GET_THREAD_INFO(r32)
-
 
         /* Check to see if there is any work to do before returning to user. */
         {
@@ -866,16 +875,18 @@ STD_ENTRY(interrupt_return)
 
         /*
          * Make sure we have all the registers saved for signal
-         * handling or single-step.  Call out to C code to figure out
-         * exactly what we need to do for each flag bit, then if
-         * necessary, reload the flags and recheck.
+         * handling, notify-resume, or single-step.  Call out to C
+         * code to figure out exactly what we need to do for each flag bit,
+         * then if necessary, reload the flags and recheck.
          */
-        push_extra_callee_saves r0
         {
          PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
-         jal    do_work_pending
+         bnz    r33, 1f
         }
-        bnz     r0, .Lresume_userspace
+        push_extra_callee_saves r0
+        movei   r33, 1
+1:      jal     do_work_pending
+        bnz     r0, .Lretry_work_pending
 
         /*
          * In the NMI case we
@@ -1180,10 +1191,12 @@ handle_syscall:
         add     r20, r20, tp
         lw      r21, r20
         addi    r21, r21, 1
-        sw      r20, r21
+        {
+         sw     r20, r21
+         GET_THREAD_INFO(r31)
+        }
 
         /* Trace syscalls, if requested. */
-        GET_THREAD_INFO(r31)
         addi    r31, r31, THREAD_INFO_FLAGS_OFFSET
         lw      r30, r31
         andi    r30, r30, _TIF_SYSCALL_TRACE
@@ -1362,7 +1375,10 @@ handle_ill:
 3:
         /* set PC and continue */
         lw      r26, r24
-        sw      r28, r26
+        {
+         sw     r28, r26
+         GET_THREAD_INFO(r0)
+        }
 
         /*
          * Clear TIF_SINGLESTEP to prevent recursion if we execute an ill.
@@ -1370,7 +1386,6 @@ handle_ill:
          * need to clear it here and can't really impose on all other arches.
          * So what's another write between friends?
          */
-        GET_THREAD_INFO(r0)
 
         addi    r1, r0, THREAD_INFO_FLAGS_OFFSET
         {
diff --git a/arch/tile/kernel/intvec_64.S b/arch/tile/kernel/intvec_64.S
index 49d9d6621682..30ae76e50c44 100644
--- a/arch/tile/kernel/intvec_64.S
+++ b/arch/tile/kernel/intvec_64.S
@@ -647,6 +647,20 @@ STD_ENTRY(interrupt_return)
         FEEDBACK_REENTER(interrupt_return)
 
         /*
+         * Use r33 to hold whether we have already loaded the callee-saves
+         * into ptregs.  We don't want to do it twice in this loop, since
+         * then we'd clobber whatever changes are made by ptrace, etc.
+         */
+        {
+         movei  r33, 0
+         move   r32, sp
+        }
+
+        /* Get base of stack in r32. */
+        EXTRACT_THREAD_INFO(r32)
+
+.Lretry_work_pending:
+        /*
          * Disable interrupts so as to make sure we don't
          * miss an interrupt that sets any of the thread flags (like
          * need_resched or sigpending) between sampling and the iret.
@@ -656,9 +670,6 @@ STD_ENTRY(interrupt_return)
         IRQ_DISABLE(r20, r21)
         TRACE_IRQS_OFF  /* Note: clobbers registers r0-r29 */
 
-        /* Get base of stack in r32; note r30/31 are used as arguments here. */
-        GET_THREAD_INFO(r32)
-
 
         /* Check to see if there is any work to do before returning to user. */
         {
@@ -674,16 +685,18 @@ STD_ENTRY(interrupt_return)
 
         /*
          * Make sure we have all the registers saved for signal
-         * handling or single-step.  Call out to C code to figure out
+         * handling or notify-resume.  Call out to C code to figure out
          * exactly what we need to do for each flag bit, then if
          * necessary, reload the flags and recheck.
          */
-        push_extra_callee_saves r0
         {
          PTREGS_PTR(r0, PTREGS_OFFSET_BASE)
-         jal    do_work_pending
+         bnez   r33, 1f
         }
-        bnez    r0, .Lresume_userspace
+        push_extra_callee_saves r0
+        movei   r33, 1
+1:      jal     do_work_pending
+        bnez    r0, .Lretry_work_pending
 
         /*
          * In the NMI case we
@@ -968,11 +981,16 @@ handle_syscall:
         shl16insli r20, r20, hw0(irq_stat + IRQ_CPUSTAT_SYSCALL_COUNT_OFFSET)
         add     r20, r20, tp
         ld4s    r21, r20
-        addi    r21, r21, 1
-        st4     r20, r21
+        {
+         addi   r21, r21, 1
+         move   r31, sp
+        }
+        {
+         st4    r20, r21
+         EXTRACT_THREAD_INFO(r31)
+        }
 
         /* Trace syscalls, if requested. */
-        GET_THREAD_INFO(r31)
         addi    r31, r31, THREAD_INFO_FLAGS_OFFSET
         ld      r30, r31
         andi    r30, r30, _TIF_SYSCALL_TRACE
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index 2d5ef617bb39..54e6c64b85cc 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -567,6 +567,10 @@ struct task_struct *__sched _switch_to(struct task_struct *prev,
  */
 int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)
 {
+        /* If we enter in kernel mode, do nothing and exit the caller loop. */
+        if (!user_mode(regs))
+                return 0;
+
         if (thread_info_flags & _TIF_NEED_RESCHED) {
                 schedule();
                 return 1;
@@ -589,8 +593,7 @@ int do_work_pending(struct pt_regs *regs, u32 thread_info_flags)
                 return 1;
         }
         if (thread_info_flags & _TIF_SINGLESTEP) {
-                if ((regs->ex1 & SPR_EX_CONTEXT_1_1__PL_MASK) == 0)
-                        single_step_once(regs);
+                single_step_once(regs);
                 return 0;
         }
         panic("work_pending: bad flags %#x\n", thread_info_flags);