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| author | Daniel Henrique Barboza <danielhb413@gmail.com> | 2021-03-23 23:50:56 +0300 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2021-03-29 05:22:18 +0300 |
| commit | d19b3ad02c2d1a9a697b7059e32fa2d97a420b15 (patch) | |
| tree | ca4977c1ed45e6db778e6fee0a81a056338e2d41 | |
| parent | dfc4ae3372182a168146745def03d877f31fcf2f (diff) | |
| download | linux-d19b3ad02c2d1a9a697b7059e32fa2d97a420b15.tar.xz | |
powerpc/pseries/hotplug-cpu: Show 'last online CPU' error in dlpar_cpu_offline()
One of the reasons that dlpar_cpu_offline can fail is when attempting to
offline the last online CPU of the kernel. This can be observed in a
pseries QEMU guest that has hotplugged CPUs. If the user offlines all
other CPUs of the guest, and a hotplugged CPU is now the last online
CPU, trying to reclaim it will fail.
The current error message in this situation returns rc with -EBUSY and a
generic explanation, e.g.:
pseries-hotplug-cpu: Failed to offline CPU PowerPC,POWER9, rc: -16
EBUSY can be caused by other conditions, such as cpu_hotplug_disable
being true. Throwing a more specific error message for this case,
instead of just "Failed to offline CPU", makes it clearer that the error
is in fact a known error situation instead of other generic/unknown
cause.
This patch adds a 'last online' check in dlpar_cpu_offline() to catch
the 'last online CPU' offline error, eturning a more informative error
message:
pseries-hotplug-cpu: Unable to remove last online CPU PowerPC,POWER9
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210323205056.52768-2-danielhb413@gmail.com
| -rw-r--r-- | arch/powerpc/platforms/pseries/hotplug-cpu.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c index 12cbffd3c2e3..ec478f8a98ff 100644 --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c @@ -271,6 +271,19 @@ static int dlpar_offline_cpu(struct device_node *dn) if (!cpu_online(cpu)) break; + /* + * device_offline() will return -EBUSY (via cpu_down()) if there + * is only one CPU left. Check it here to fail earlier and with a + * more informative error message, while also retaining the + * cpu_add_remove_lock to be sure that no CPUs are being + * online/offlined during this check. + */ + if (num_online_cpus() == 1) { + pr_warn("Unable to remove last online CPU %pOFn\n", dn); + rc = -EBUSY; + goto out_unlock; + } + cpu_maps_update_done(); rc = device_offline(get_cpu_device(cpu)); if (rc) @@ -283,6 +296,7 @@ static int dlpar_offline_cpu(struct device_node *dn) thread); } } +out_unlock: cpu_maps_update_done(); out: |