[PATCH] ppc32: Fix racy access to TI_FLAGS
From: Benjamin Herrenschmidt
Date: Thu Mar 25 2004 - 22:26:28 EST
Hi !
The ppc32 syscall entry code could access the thread info flags
in a racy way, thus potentially losing bits sets there at interrupt
time or by another CPU, like NEED_RESCHED or SIGPENDING (ouch !).
This fixes it by moving the potentially racy bit to a different
field (I preferred that rather than turning the access into an
atomic operation for performances reasons).
Please apply,
Ben.
diff -urN linux-2.5/arch/ppc/kernel/entry.S linuxppc-2.5-benh/arch/ppc/kernel/entry.S
--- linux-2.5/arch/ppc/kernel/entry.S 2004-03-01 18:11:11.000000000 +1100
+++ linuxppc-2.5-benh/arch/ppc/kernel/entry.S 2004-03-25 14:10:41.000000000 +1100
@@ -171,9 +171,10 @@
bl do_show_syscall
#endif /* SHOW_SYSCALLS */
rlwinm r10,r1,0,0,18 /* current_thread_info() */
+ lwz r11,TI_LOCAL_FLAGS(r10)
+ rlwinm r11,r11,0,~_TIFL_FORCE_NOERROR
+ stw r11,TI_LOCAL_FLAGS(r10)
lwz r11,TI_FLAGS(r10)
- rlwinm r11,r11,0,~_TIF_FORCE_NOERROR
- stw r11,TI_FLAGS(r10)
andi. r11,r11,_TIF_SYSCALL_TRACE
bne- syscall_dotrace
syscall_dotrace_cont:
@@ -196,8 +197,8 @@
cmpl 0,r3,r11
rlwinm r12,r1,0,0,18 /* current_thread_info() */
blt+ 30f
- lwz r11,TI_FLAGS(r12)
- andi. r11,r11,_TIF_FORCE_NOERROR
+ lwz r11,TI_LOCAL_FLAGS(r12)
+ andi. r11,r11,_TIFL_FORCE_NOERROR
bne 30f
neg r3,r3
lwz r10,_CCR(r1) /* Set SO bit in CR */
diff -urN linux-2.5/include/asm-ppc/ptrace.h linuxppc-2.5-benh/include/asm-ppc/ptrace.h
--- linux-2.5/include/asm-ppc/ptrace.h 2004-03-01 18:13:06.000000000 +1100
+++ linuxppc-2.5-benh/include/asm-ppc/ptrace.h 2004-03-25 14:02:44.000000000 +1100
@@ -49,7 +49,10 @@
#define instruction_pointer(regs) ((regs)->nip)
#define user_mode(regs) (((regs)->msr & MSR_PR) != 0)
-#define force_successful_syscall_return() set_thread_flag(TIF_FORCE_NOERROR)
+#define force_successful_syscall_return() \
+ do { \
+ current_thread_info()->local_flags |= _TIFL_FORCE_NOERROR; \
+ } while(0)
/*
* We use the least-significant bit of the trap field to indicate
diff -urN linux-2.5/include/asm-ppc/thread_info.h linuxppc-2.5-benh/include/asm-ppc/thread_info.h
--- linux-2.5/include/asm-ppc/thread_info.h 2004-03-01 18:13:06.000000000 +1100
+++ linuxppc-2.5-benh/include/asm-ppc/thread_info.h 2004-03-25 14:03:56.000000000 +1100
@@ -18,6 +18,7 @@
struct task_struct *task; /* main task structure */
struct exec_domain *exec_domain; /* execution domain */
unsigned long flags; /* low level flags */
+ unsigned long local_flags; /* non-racy flags */
int cpu; /* cpu we're on */
int preempt_count;
struct restart_block restart_block;
@@ -28,6 +29,7 @@
.task = &tsk, \
.exec_domain = &default_exec_domain, \
.flags = 0, \
+ .local_flags = 0, \
.cpu = 0, \
.preempt_count = 1, \
.restart_block = { \
@@ -69,8 +71,9 @@
#define TI_TASK 0
#define TI_EXECDOMAIN 4
#define TI_FLAGS 8
-#define TI_CPU 12
-#define TI_PREEMPT 16
+#define TI_LOCAL_FLAGS 12
+#define TI_CPU 16
+#define TI_PREEMPT 20
#define PREEMPT_ACTIVE 0x4000000
@@ -83,16 +86,22 @@
#define TIF_NEED_RESCHED 3 /* rescheduling necessary */
#define TIF_POLLING_NRFLAG 4 /* true if poll_idle() is polling
TIF_NEED_RESCHED */
-#define TIF_FORCE_NOERROR 5 /* don't return error from current
- syscall even if result < 0 */
-
/* as above, but as bit values */
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
#define _TIF_SIGPENDING (1<<TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED)
#define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG)
-#define _TIF_FORCE_NOERROR (1<<TIF_FORCE_NOERROR)
+
+/*
+ * Non racy (local) flags bit numbers
+ */
+#define TIFL_FORCE_NOERROR 0 /* don't return error from current
+ syscall even if result < 0 */
+
+/* as above, but as bit values */
+#define _TIFL_FORCE_NOERROR (1<<TIFL_FORCE_NOERROR)
+
#endif /* __KERNEL__ */
-
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