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powerpc: Only obtain cpu_hotplug_lock if called by rtasd 

Calling arch_update_cpu_topology from a CPU hotplug state machine callback
hits a deadlock because the function tries to get a read lock on
cpu_hotplug_lock while the state machine still holds a write lock on it.

Since all callers of arch_update_cpu_topology except rtasd already hold
cpu_hotplug_lock, this patch changes the function to use
stop_machine_cpuslocked and creates a separate function for rtasd which
still tries to obtain the lock.

Michael Bringmann investigated the bug and provided a detailed analysis
of the deadlock on this previous RFC for an alternate solution:

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: John Allen <jallen@linux.vnet.ibm.com>
Cc: Michael Bringmann <mwb@linux.vnet.ibm.com>
Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1497996510-4032-1-git-send-email-bauerman@linux.vnet.ibm.com
Link: https://patchwork.ozlabs.org/patch/771293/
This commit is contained in:
Thiago Jung Bauermann 2017-06-20 19:08:30 -03:00 committed by Thomas Gleixner
parent 1b3b22507e
commit 3e401f7a2e
3 changed files with 26 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/powerpc/include/asm/topology.h
View File

@ -43,6 +43,7 @@ extern void __init dump_numa_cpu_topology(void);
extern int sysfs_add_device_to_node(struct device *dev, int nid);
extern void sysfs_remove_device_from_node(struct device *dev, int nid);
extern int numa_update_cpu_topology(bool cpus_locked);
#else
@ -57,6 +58,11 @@ static inline void sysfs_remove_device_from_node(struct device *dev,
int nid)
{
}
static inline int numa_update_cpu_topology(bool cpus_locked)
{
return 0;
}
#endif /* CONFIG_NUMA */
#if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)

2
arch/powerpc/kernel/rtasd.c
View File

@ -283,7 +283,7 @@ static void prrn_work_fn(struct work_struct *work)
* the RTAS event.
*/
pseries_devicetree_update(-prrn_update_scope);
arch_update_cpu_topology();
numa_update_cpu_topology(false);
}
static DECLARE_WORK(prrn_work, prrn_work_fn);

22
arch/powerpc/mm/numa.c
View File

@ -1311,8 +1311,10 @@ static int update_lookup_table(void *data)
/*
* Update the node maps and sysfs entries for each cpu whose home node
* has changed. Returns 1 when the topology has changed, and 0 otherwise.
*
* cpus_locked says whether we already hold cpu_hotplug_lock.
*/
int arch_update_cpu_topology(void)
int numa_update_cpu_topology(bool cpus_locked)
{
unsigned int cpu, sibling, changed = 0;
struct topology_update_data *updates, *ud;
@ -1400,15 +1402,23 @@ int arch_update_cpu_topology(void)
if (!cpumask_weight(&updated_cpus))
goto out;
stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
if (cpus_locked)
stop_machine_cpuslocked(update_cpu_topology, &updates[0],
&updated_cpus);
else
stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
/*
* Update the numa-cpu lookup table with the new mappings, even for
* offline CPUs. It is best to perform this update from the stop-
* machine context.
*/
stop_machine(update_lookup_table, &updates[0],
if (cpus_locked)
stop_machine_cpuslocked(update_lookup_table, &updates[0],
cpumask_of(raw_smp_processor_id()));
else
stop_machine(update_lookup_table, &updates[0],
cpumask_of(raw_smp_processor_id()));
for (ud = &updates[0]; ud; ud = ud->next) {
unregister_cpu_under_node(ud->cpu, ud->old_nid);
@ -1426,6 +1436,12 @@ int arch_update_cpu_topology(void)
return changed;
}
int arch_update_cpu_topology(void)
{
lockdep_assert_cpus_held();
return numa_update_cpu_topology(true);
}
static void topology_work_fn(struct work_struct *work)
{
rebuild_sched_domains();