s390: fix race on TIF_MCCK_PENDING
There is a small race window in the __switch_to code in regard to
the transfer of the TIF_MCCK_PENDING bit from the previous to the
next task. The bit is transferred before the task struct pointer
and the thread-info pointer for the next task has been stored to
lowcore. If a machine check sets the TIF_MCCK_PENDING bit between
the transfer code and the store of current/thread_info the bit
is still set for the previous task. And if the previous task has
terminated it can get lost. The effect is that a pending CRW is
not retrieved until the next machine checks sets TIF_MCCK_PENDING.
To fix this reorder __switch_to to first store the task struct
and thread-info pointer and then do the transfer of the bit.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 74ee563..1ae93b5 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -145,22 +145,23 @@
* gpr2 = prev
*/
ENTRY(__switch_to)
+ stm %r6,%r15,__SF_GPRS(%r15) # store gprs of prev task
+ st %r15,__THREAD_ksp(%r2) # store kernel stack of prev
l %r4,__THREAD_info(%r2) # get thread_info of prev
l %r5,__THREAD_info(%r3) # get thread_info of next
+ lr %r15,%r5
+ ahi %r15,STACK_SIZE # end of kernel stack of next
+ st %r3,__LC_CURRENT # store task struct of next
+ st %r5,__LC_THREAD_INFO # store thread info of next
+ st %r15,__LC_KERNEL_STACK # store end of kernel stack
+ lctl %c4,%c4,__TASK_pid(%r3) # load pid to control reg. 4
+ mvc __LC_CURRENT_PID(4,%r0),__TASK_pid(%r3) # store pid of next
+ l %r15,__THREAD_ksp(%r3) # load kernel stack of next
tm __TI_flags+3(%r4),_TIF_MCCK_PENDING # machine check pending?
jz 0f
ni __TI_flags+3(%r4),255-_TIF_MCCK_PENDING # clear flag in prev
oi __TI_flags+3(%r5),_TIF_MCCK_PENDING # set it in next
-0: stm %r6,%r15,__SF_GPRS(%r15) # store gprs of prev task
- st %r15,__THREAD_ksp(%r2) # store kernel stack of prev
- l %r15,__THREAD_ksp(%r3) # load kernel stack of next
- lctl %c4,%c4,__TASK_pid(%r3) # load pid to control reg. 4
- lm %r6,%r15,__SF_GPRS(%r15) # load gprs of next task
- st %r3,__LC_CURRENT # store task struct of next
- mvc __LC_CURRENT_PID(4,%r0),__TASK_pid(%r3) # store pid of next
- st %r5,__LC_THREAD_INFO # store thread info of next
- ahi %r5,STACK_SIZE # end of kernel stack of next
- st %r5,__LC_KERNEL_STACK # store end of kernel stack
+0: lm %r6,%r15,__SF_GPRS(%r15) # load gprs of next task
br %r14
__critical_start:
diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index 02bf601..229fe1d 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -164,22 +164,23 @@
* gpr2 = prev
*/
ENTRY(__switch_to)
+ stmg %r6,%r15,__SF_GPRS(%r15) # store gprs of prev task
+ stg %r15,__THREAD_ksp(%r2) # store kernel stack of prev
lg %r4,__THREAD_info(%r2) # get thread_info of prev
lg %r5,__THREAD_info(%r3) # get thread_info of next
+ lgr %r15,%r5
+ aghi %r15,STACK_SIZE # end of kernel stack of next
+ stg %r3,__LC_CURRENT # store task struct of next
+ stg %r5,__LC_THREAD_INFO # store thread info of next
+ stg %r15,__LC_KERNEL_STACK # store end of kernel stack
+ lctl %c4,%c4,__TASK_pid(%r3) # load pid to control reg. 4
+ mvc __LC_CURRENT_PID+4(4,%r0),__TASK_pid(%r3) # store pid of next
+ lg %r15,__THREAD_ksp(%r3) # load kernel stack of next
tm __TI_flags+7(%r4),_TIF_MCCK_PENDING # machine check pending?
jz 0f
ni __TI_flags+7(%r4),255-_TIF_MCCK_PENDING # clear flag in prev
oi __TI_flags+7(%r5),_TIF_MCCK_PENDING # set it in next
-0: stmg %r6,%r15,__SF_GPRS(%r15) # store gprs of prev task
- stg %r15,__THREAD_ksp(%r2) # store kernel stack of prev
- lg %r15,__THREAD_ksp(%r3) # load kernel stack of next
- lctl %c4,%c4,__TASK_pid(%r3) # load pid to control reg. 4
- lmg %r6,%r15,__SF_GPRS(%r15) # load gprs of next task
- stg %r3,__LC_CURRENT # store task struct of next
- mvc __LC_CURRENT_PID+4(4,%r0),__TASK_pid(%r3) # store pid of next
- stg %r5,__LC_THREAD_INFO # store thread info of next
- aghi %r5,STACK_SIZE # end of kernel stack of next
- stg %r5,__LC_KERNEL_STACK # store end of kernel stack
+0: lmg %r6,%r15,__SF_GPRS(%r15) # load gprs of next task
br %r14
__critical_start: