* [PATCH v2 0/1] show 'last online CPU' error in dlpar_cpu_offline() @ 2021-03-23 20:50 Daniel Henrique Barboza 2021-03-23 20:50 ` [PATCH v2 1/1] hotplug-cpu.c: " Daniel Henrique Barboza 2021-03-31 1:09 ` [PATCH v2 0/1] " Michael Ellerman 0 siblings, 2 replies; 5+ messages in thread From: Daniel Henrique Barboza @ 2021-03-23 20:50 UTC (permalink / raw) To: linuxppc-dev; +Cc: Daniel Henrique Barboza changes in v2 after Michael Ellerman review: - moved the verification code from dlpar_cpu_remove() to dlpar_cpu_offline(), while holding cpu_add_remove_lock - reworded the commit message and code comment v1 link: https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210305173845.451158-1-danielhb413@gmail.com/ Daniel Henrique Barboza (1): hotplug-cpu.c: show 'last online CPU' error in dlpar_cpu_offline() arch/powerpc/platforms/pseries/hotplug-cpu.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) -- 2.30.2 ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v2 1/1] hotplug-cpu.c: show 'last online CPU' error in dlpar_cpu_offline() 2021-03-23 20:50 [PATCH v2 0/1] show 'last online CPU' error in dlpar_cpu_offline() Daniel Henrique Barboza @ 2021-03-23 20:50 ` Daniel Henrique Barboza 2021-03-26 5:24 ` Daniel Axtens 2021-03-31 1:09 ` [PATCH v2 0/1] " Michael Ellerman 1 sibling, 1 reply; 5+ messages in thread From: Daniel Henrique Barboza @ 2021-03-23 20:50 UTC (permalink / raw) To: linuxppc-dev; +Cc: Daniel Henrique Barboza 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. See [1] for an example. 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 [1] https://bugzilla.redhat.com/1911414 Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com> --- arch/powerpc/platforms/pseries/hotplug-cpu.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c index 12cbffd3c2e3..3ac7e904385c 100644 --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c @@ -271,6 +271,18 @@ 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 +295,7 @@ static int dlpar_offline_cpu(struct device_node *dn) thread); } } +out_unlock: cpu_maps_update_done(); out: -- 2.30.2 ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2 1/1] hotplug-cpu.c: show 'last online CPU' error in dlpar_cpu_offline() 2021-03-23 20:50 ` [PATCH v2 1/1] hotplug-cpu.c: " Daniel Henrique Barboza @ 2021-03-26 5:24 ` Daniel Axtens 2021-03-26 14:08 ` Daniel Henrique Barboza 0 siblings, 1 reply; 5+ messages in thread From: Daniel Axtens @ 2021-03-26 5:24 UTC (permalink / raw) To: Daniel Henrique Barboza, linuxppc-dev; +Cc: Daniel Henrique Barboza Hi Daniel, Two small nitpicks: > This patch adds a 'last online' check in dlpar_cpu_offline() to catch > the 'last online CPU' offline error, eturning a more informative error ^--- s/eturning/returning/; > + /* 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. */ Checkpatch has a small issue with this comment: WARNING: Block comments use a trailing */ on a separate line #50: FILE: arch/powerpc/platforms/pseries/hotplug-cpu.c:279: + * check. */ Apart from that, this patch seems sane to me, but I haven't been able to test it. Kind regards, Daniel ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 1/1] hotplug-cpu.c: show 'last online CPU' error in dlpar_cpu_offline() 2021-03-26 5:24 ` Daniel Axtens @ 2021-03-26 14:08 ` Daniel Henrique Barboza 0 siblings, 0 replies; 5+ messages in thread From: Daniel Henrique Barboza @ 2021-03-26 14:08 UTC (permalink / raw) To: Daniel Axtens, linuxppc-dev Hey Daniel, On 3/26/21 2:24 AM, Daniel Axtens wrote: > Hi Daniel, > > Two small nitpicks: > >> This patch adds a 'last online' check in dlpar_cpu_offline() to catch >> the 'last online CPU' offline error, eturning a more informative error > ^--- s/eturning/returning/; > > >> + /* 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. */ > > Checkpatch has a small issue with this comment: > > WARNING: Block comments use a trailing */ on a separate line > #50: FILE: arch/powerpc/platforms/pseries/hotplug-cpu.c:279: > + * check. */ > > Apart from that, this patch seems sane to me, but I haven't been able to > test it. Thanks for the review, and for letting me know of the existence of 'scripts/checkpatch.pl' to verify the patches before posting. I'll send a v3. Thanks, DHB > > Kind regards, > Daniel > ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 0/1] show 'last online CPU' error in dlpar_cpu_offline() 2021-03-23 20:50 [PATCH v2 0/1] show 'last online CPU' error in dlpar_cpu_offline() Daniel Henrique Barboza 2021-03-23 20:50 ` [PATCH v2 1/1] hotplug-cpu.c: " Daniel Henrique Barboza @ 2021-03-31 1:09 ` Michael Ellerman 1 sibling, 0 replies; 5+ messages in thread From: Michael Ellerman @ 2021-03-31 1:09 UTC (permalink / raw) To: linuxppc-dev, Daniel Henrique Barboza On Tue, 23 Mar 2021 17:50:55 -0300, Daniel Henrique Barboza wrote: > changes in v2 after Michael Ellerman review: > - moved the verification code from dlpar_cpu_remove() to > dlpar_cpu_offline(), while holding cpu_add_remove_lock > - reworded the commit message and code comment > v1 link: > https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210305173845.451158-1-danielhb413@gmail.com/ > > [...] Applied to powerpc/next. [1/1] hotplug-cpu.c: show 'last online CPU' error in dlpar_cpu_offline() https://git.kernel.org/powerpc/c/d19b3ad02c2d1a9a697b7059e32fa2d97a420b15 cheers ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-03-31 1:14 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-03-23 20:50 [PATCH v2 0/1] show 'last online CPU' error in dlpar_cpu_offline() Daniel Henrique Barboza 2021-03-23 20:50 ` [PATCH v2 1/1] hotplug-cpu.c: " Daniel Henrique Barboza 2021-03-26 5:24 ` Daniel Axtens 2021-03-26 14:08 ` Daniel Henrique Barboza 2021-03-31 1:09 ` [PATCH v2 0/1] " Michael Ellerman
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