Commit 3e401f7a authored by Thiago Jung Bauermann's avatar Thiago Jung Bauermann Committed by Thomas Gleixner

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: default avatarThiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarMichael 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/
parent 1b3b2250
......@@ -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)
......
......@@ -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);
......
......@@ -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;
......@@ -1400,6 +1402,10 @@ int arch_update_cpu_topology(void)
if (!cpumask_weight(&updated_cpus))
goto out;
if (cpus_locked)
stop_machine_cpuslocked(update_cpu_topology, &updates[0],
&updated_cpus);
else
stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
/*
......@@ -1407,6 +1413,10 @@ int arch_update_cpu_topology(void)
* offline CPUs. It is best to perform this update from the stop-
* machine context.
*/
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()));
......@@ -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();
......
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