tree d863e72afaedfd89939c45ac95c9e02a2c585aa7
parent 698fd6a2c3ca05ec796072defb5c415289a86cdc
author Heiko Carstens <heiko.carstens@de.ibm.com> 1290675165 +0100
committer Martin Schwidefsky <sky@mschwide.boeblingen.de.ibm.com> 1290675179 +0100

[S390] nmi: fix clock comparator revalidation

On each machine check all registers are revalidated. The save area for
the clock comparator however only contains the upper most seven bytes
of the former contents, if valid.
Therefore the machine check handler uses a store clock instruction to
get the current time and writes that to the clock comparator register
which in turn will generate an immediate timer interrupt.
However within the lowcore the expected time of the next timer
interrupt is stored. If the interrupt happens before that time the
handler won't be called. In turn the clock comparator won't be
reprogrammed and therefore the interrupt condition stays pending which
causes an interrupt loop until the expected time is reached.

On NOHZ machines this can result in unresponsive machines since the
time of the next expected interrupted can be a couple of days in the
future.

To fix this just revalidate the clock comparator register with the
expected value.
In addition the special handling for udelay must be changed as well.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>