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>

diff --git a/arch/tile/include/asm/thread_info.h b/arch/tile/include/asm/thread_info.h
index bc4f562..7594764 100644 (file)
--- 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 5d56a1e..6943515 100644 (file)
--- 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 49d9d66..30ae76e 100644 (file)
--- 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 2d5ef61..54e6c64 100644 (file)
--- 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);