[PATCH] powerpc/rtas: retry when cpu offline races with suspend/migration
patch-notifications at ellerman.id.au
Thu Jul 4 00:27:04 AEST 2019
On Fri, 2019-06-21 at 06:05:18 UTC, 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
> 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.
> Fixes: dfd718a2ed1f ("powerpc/rtas: Fix a potential race between CPU-Offline & Migration")
> Signed-off-by: Nathan Lynch <nathanl at linux.ibm.com>
Applied to powerpc next, thanks.
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