On 2019-06-21 00:05, Nathan Lynch wrote:
The protocol for suspending or migrating an LPAR requires all present
processor threads to enter H_JOIN. So if we have threads offline, we
have to temporarily bring them up. This can race with administrator
actions such as SMT state changes. As of dfd718a2ed1f ("powerpc/rtas:
Fix a potential race between CPU-Offline & Migration"),
rtas_ibm_suspend_me() accounts for this, but errors out with -EBUSY
for what almost certainly is a transient condition in any reasonable
scenario.
Callers of rtas_ibm_suspend_me() already retry when -EAGAIN is
returned, and it is typical during a migration for that to happen
repeatedly for several minutes polling the H_VASI_STATE hcall result
before proceeding to the next stage.
So return -EAGAIN instead of -EBUSY when this race is
encountered. Additionally: logging this event is still appropriate but
use pr_info instead of pr_err; and remove use of unlikely() while here
as this is not a hot path at all.
Looks good, since it's not a hot path anyway, so unlikely() should
benefit from optimize compiler path, and should stay. No?
Mingming
Fixes: dfd718a2ed1f ("powerpc/rtas: Fix a potential race between
CPU-Offline & Migration")
Signed-off-by: Nathan Lynch <nath...@linux.ibm.com>
---
arch/powerpc/kernel/rtas.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index fbc676160adf..9b4d2a2ffb4f 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -984,10 +984,9 @@ int rtas_ibm_suspend_me(u64 handle)
cpu_hotplug_disable();
/* Check if we raced with a CPU-Offline Operation */
- if (unlikely(!cpumask_equal(cpu_present_mask, cpu_online_mask))) {
- pr_err("%s: Raced against a concurrent CPU-Offline\n",
- __func__);
- atomic_set(&data.error, -EBUSY);
+ if (!cpumask_equal(cpu_present_mask, cpu_online_mask)) {
+ pr_info("%s: Raced against a concurrent CPU-Offline\n",
__func__);
+ atomic_set(&data.error, -EAGAIN);
goto out_hotplug_enable;
}
