Subject: [PATCH] flow_cache_flush soft lockup with heavy ipsec traffic

From: Maris Paupe <[email-masked]>
Date: Wed, 09 Nov 2011 14:21:12 +0200

During ipsec packet processing flow_cache_flush() may get called which 
creates flow_cache_gc_taklet(), this function is guarded by mutex and 
waits until all tasklets are finished before releasing it, another 
softirq may happen during flow_cache_gc_taklet(), in case when this irq 
is packet reading from a device, it can happen that flow_cache_flush() 
gets called again and a deadlock occurs.
Here i purpose a simple fix to this problem by disabling softirqs during 
tasklet process. It could also be fixed in ipsec processing code, but I 
am too unfamiliar with it to touch it.

Signed-off-by: Maris Paupe <[email-masked]>

diff --git a/net/core/flow.c b/net/core/flow.c
index 8ae42de..19ff283 100644
--- a/net/core/flow.c
+++ b/net/core/flow.c
@@ -105,6 +105,7 @@ static void flow_cache_gc_task(struct work_struct *work)
  	struct list_head gc_list;
  	struct flow_cache_entry *fce, *n;

+	local_bh_disable();
  	INIT_LIST_HEAD(&gc_list);
  	spin_lock_bh(&flow_cache_gc_lock);
  	list_splice_tail_init(&flow_cache_gc_list, &gc_list);
@@ -112,6 +113,7 @@ static void flow_cache_gc_task(struct work_struct *work)

  	list_for_each_entry_safe(fce, n, &gc_list, u.gc_list)
  		flow_entry_kill(fce);
+	local_bh_enable();
  }
  static DECLARE_WORK(flow_cache_gc_work, flow_cache_gc_task);