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authorGerald Schaefer <gerald.schaefer@de.ibm.com>2019-01-09 13:00:03 +0100
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2019-01-11 17:12:02 +0100
commitb7cb707c373094ce4008d4a6ac9b6b366ec52da5 (patch)
tree1b7129f3190ccfcadcb4330677b0f27b245f1d2b /drivers/s390
parenta38662084c8bdb829ff486468c7ea801c13fcc34 (diff)
s390/smp: fix CPU hotplug deadlock with CPU rescan
smp_rescan_cpus() is called without the device_hotplug_lock, which can lead to a dedlock when a new CPU is found and immediately set online by a udev rule. This was observed on an older kernel version, where the cpu_hotplug_begin() loop was still present, and it resulted in hanging chcpu and systemd-udev processes. This specific deadlock will not show on current kernels. However, there may be other possible deadlocks, and since smp_rescan_cpus() can still trigger a CPU hotplug operation, the device_hotplug_lock should be held. For reference, this was the deadlock with the old cpu_hotplug_begin() loop: chcpu (rescan) systemd-udevd echo 1 > /sys/../rescan -> smp_rescan_cpus() -> (*) get_online_cpus() (increases refcount) -> smp_add_present_cpu() (new CPU found) -> register_cpu() -> device_add() -> udev "add" event triggered -----------> udev rule sets CPU online -> echo 1 > /sys/.../online -> lock_device_hotplug_sysfs() (this is missing in rescan path) -> device_online() -> (**) device_lock(new CPU dev) -> cpu_up() -> cpu_hotplug_begin() (loops until refcount == 0) -> deadlock with (*) -> bus_probe_device() -> device_attach() -> device_lock(new CPU dev) -> deadlock with (**) Fix this by taking the device_hotplug_lock in the CPU rescan path. Cc: <stable@vger.kernel.org> Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'drivers/s390')
-rw-r--r--drivers/s390/char/sclp_config.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/s390/char/sclp_config.c b/drivers/s390/char/sclp_config.c
index 194ffd5c8580..039b2074db7e 100644
--- a/drivers/s390/char/sclp_config.c
+++ b/drivers/s390/char/sclp_config.c
@@ -60,7 +60,9 @@ static void sclp_cpu_capability_notify(struct work_struct *work)
static void __ref sclp_cpu_change_notify(struct work_struct *work)
{
+ lock_device_hotplug();
smp_rescan_cpus();
+ unlock_device_hotplug();
}
static void sclp_conf_receiver_fn(struct evbuf_header *evbuf)