Messages in this thread |  | | Date | Thu, 14 Sep 2023 13:17:27 -0700 | From | Ira Weiny <> | Subject | Re: [PATCH] nd_btt: Make BTT lanes preemptible |
| |
Tomáš Glozar wrote: > From: Tomas Glozar <tglozar@redhat.com> > > nd_region_acquire_lane uses get_cpu, which disables preemption. This is > an issue on PREEMPT_RT kernels, since btt_write_pg and also > nd_region_acquire_lane itself take a spin lock, resulting in BUG: > sleeping function called from invalid context.
Is the bug in 1 of 2 places?
1) When btt_write_pg()->lock_map() (when the number of lanes is < number of cpus) and the lane is acquired is called?
*or*
2) When nd_region_acquire_lane() internally trys to take it's lock?
A copy/paste of the BUG observed would have been more clear I think.
Regardless I *think* this is ok but I'm worried I don't fully understand what the problem is.
Ira
> > Fix the issue by replacing get_cpu with smp_process_id and > migrate_disable when needed. This makes BTT operations preemptible, thus > permitting the use of spin_lock. > > Fixes: 5212e11fde4d ("nd_btt: atomic sector updates") > Signed-off-by: Tomas Glozar <tglozar@redhat.com> > --- > drivers/nvdimm/region_devs.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c > index 0a81f87f6f6c..e2f1fb99707f 100644 > --- a/drivers/nvdimm/region_devs.c > +++ b/drivers/nvdimm/region_devs.c > @@ -939,7 +939,8 @@ unsigned int nd_region_acquire_lane(struct nd_region *nd_region) > { > unsigned int cpu, lane; > > - cpu = get_cpu(); > + migrate_disable(); > + cpu = smp_processor_id(); > if (nd_region->num_lanes < nr_cpu_ids) { > struct nd_percpu_lane *ndl_lock, *ndl_count; > > @@ -958,16 +959,15 @@ EXPORT_SYMBOL(nd_region_acquire_lane); > void nd_region_release_lane(struct nd_region *nd_region, unsigned int lane) > { > if (nd_region->num_lanes < nr_cpu_ids) { > - unsigned int cpu = get_cpu(); > + unsigned int cpu = smp_processor_id(); > struct nd_percpu_lane *ndl_lock, *ndl_count; > > ndl_count = per_cpu_ptr(nd_region->lane, cpu); > ndl_lock = per_cpu_ptr(nd_region->lane, lane); > if (--ndl_count->count == 0) > spin_unlock(&ndl_lock->lock); > - put_cpu(); > } > - put_cpu(); > + migrate_enable(); > } > EXPORT_SYMBOL(nd_region_release_lane); > > -- > 2.39.3 >
|  |