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| author | Gerald Schaefer <gerald.schaefer@de.ibm.com> | 2019-01-09 13:00:03 +0100 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2019-01-11 17:12:02 +0100 |
| commit | b7cb707c373094ce4008d4a6ac9b6b366ec52da5 (patch) | |
| tree | 1b7129f3190ccfcadcb4330677b0f27b245f1d2b | |
| parent | a38662084c8bdb829ff486468c7ea801c13fcc34 (diff) | |
| download | linux-b7cb707c373094ce4008d4a6ac9b6b366ec52da5.tar.bz2 | |
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>
| -rw-r--r-- | arch/s390/kernel/smp.c | 4 | ||||
| -rw-r--r-- | drivers/s390/char/sclp_config.c | 2 |
2 files changed, 6 insertions, 0 deletions
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index f82b3d3c36e2..307a1c86ea21 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -1166,7 +1166,11 @@ static ssize_t __ref rescan_store(struct device *dev, { int rc; + rc = lock_device_hotplug_sysfs(); + if (rc) + return rc; rc = smp_rescan_cpus(); + unlock_device_hotplug(); return rc ? rc : count; } static DEVICE_ATTR_WO(rescan); 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) |