tree 5f57e3581729dfad7a7999ee24fd044b47018b8e
parent e5b8d7553f87d939295e9eb0ca699c0030dc5ff1
author Martin Schwidefsky <schwidefsky@de.ibm.com> 1337066406 +0200
committer Martin Schwidefsky <schwidefsky@de.ibm.com> 1337172166 +0200

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>