4.9-stable review patch. If anyone has any objections, please let me know.
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From: Vitaly Kuznetsov vkuznets@redhat.com
[ Upstream commit 87dffe86d406bee8782cac2db035acb9a28620a7 ]
When guest receives a sysrq request from the host it acknowledges it by writing '\0' to control/sysrq xenstore node. This, however, make xenstore watch fire again but xenbus_scanf() fails to parse empty value with "%c" format string:
sysrq: SysRq : Emergency Sync Emergency Sync complete xen:manage: Error -34 reading sysrq code in control/sysrq
Ignore -ERANGE the same way we already ignore -ENOENT, empty value in control/sysrq is totally legal.
Signed-off-by: Vitaly Kuznetsov vkuznets@redhat.com Reviewed-by: Wei Liu wei.liu2@citrix.com Signed-off-by: Boris Ostrovsky boris.ostrovsky@oracle.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/xen/manage.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/drivers/xen/manage.c +++ b/drivers/xen/manage.c @@ -282,9 +282,11 @@ static void sysrq_handler(struct xenbus_ /* * The Xenstore watch fires directly after registering it and * after a suspend/resume cycle. So ENOENT is no error but - * might happen in those cases. + * might happen in those cases. ERANGE is observed when we get + * an empty value (''), this happens when we acknowledge the + * request by writing '\0' below. */ - if (err != -ENOENT) + if (err != -ENOENT && err != -ERANGE) pr_err("Error %d reading sysrq code in control/sysrq\n", err); xenbus_transaction_end(xbt, 1);