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| author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2012-05-15 07:20:06 (GMT) |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2012-05-16 12:42:46 (GMT) |
| commit | eda0c6d6b04d3cf72f5e8d656e39bffe3568e6db (patch) | |
| tree | 5f57e3581729dfad7a7999ee24fd044b47018b8e /arch/s390/kernel/entry64.S | |
| parent | e5b8d7553f87d939295e9eb0ca699c0030dc5ff1 (diff) | |
| download | linux-eda0c6d6b04d3cf72f5e8d656e39bffe3568e6db.tar.xz | |
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>
Diffstat (limited to 'arch/s390/kernel/entry64.S')
| -rw-r--r-- | arch/s390/kernel/entry64.S | 21 |
1 files changed, 11 insertions, 10 deletions
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 @@ _TIF_EXIT_SIE = (_TIF_SIGPENDING | _TIF_NEED_RESCHED | _TIF_MCCK_PENDING) * 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: |