[PATCH 13/19] MM: set PF_FSTRANS while allocating per-cpu memory to avoid deadlock.

[NeilBrown]

lockdep reports a locking chain

  sk_lock-AF_INET --> rtnl_mutex --> pcpu_alloc_mutex

As sk_lock may be needed to reclaim memory, allowing that
reclaim while pcu_alloc_mutex is held can lead to deadlock.
So set PF_FSTRANS while it is help to avoid the FS reclaim.

pcpu_alloc_mutex can be taken when rtnl_mutex is held:

    [<ffffffff8117f979>] pcpu_alloc+0x49/0x960
    [<ffffffff8118029b>] __alloc_percpu+0xb/0x10
    [<ffffffff8193b9f7>] loopback_dev_init+0x17/0x60
    [<ffffffff81aaf30c>] register_netdevice+0xec/0x550
    [<ffffffff81aaf785>] register_netdev+0x15/0x30

Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
 mm/percpu.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/percpu.c b/mm/percpu.c
index 036cfe07050f..77dd24032f41 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -712,6 +712,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved)
 	int slot, off, new_alloc;
 	unsigned long flags;
 	void __percpu *ptr;
+	unsigned int pflags;
 
 	if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
 		WARN(true, "illegal size (%zu) or align (%zu) for "
@@ -720,6 +721,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved)
 	}
 
 	mutex_lock(&pcpu_alloc_mutex);
+	current_set_flags_nested(&pflags, PF_FSTRANS);
 	spin_lock_irqsave(&pcpu_lock, flags);
 
 	/* serve reserved allocations from the reserved chunk if available */
@@ -801,6 +803,7 @@ area_found:
 		goto fail_unlock;
 	}
 
+	current_restore_flags_nested(&pflags, PF_FSTRANS);
 	mutex_unlock(&pcpu_alloc_mutex);
 
 	/* return address relative to base address */
@@ -811,6 +814,7 @@ area_found:
 fail_unlock:
 	spin_unlock_irqrestore(&pcpu_lock, flags);
 fail_unlock_mutex:
+	current_restore_flags_nested(&pflags, PF_FSTRANS);
 	mutex_unlock(&pcpu_alloc_mutex);
 	if (warn_limit) {
 		pr_warning("PERCPU: allocation failed, size=%zu align=%zu, "


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