From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: [PATCH block/for-4.3] writeback: explain why @inode is allowed to be
 NULL for inode_congested()
Date: Sat, 4 Jul 2015 11:12:00 -0400
Message-ID: <20150704151200.GA13251@mtj.duckdns.org>
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 <20150703121721.GJ23329@quack.suse.cz>
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To: Jan Kara <jack@suse.cz>
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Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Jan Kara <jack@suse.cz>
---
Hello,

So, something like this.  I'll resend this patch as part of a patch
series once -rc1 drops.

Thanks.

 fs/fs-writeback.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -700,7 +700,7 @@ void wbc_account_io(struct writeback_con
 
 /**
  * inode_congested - test whether an inode is congested
- * @inode: inode to test for congestion
+ * @inode: inode to test for congestion (may be NULL)
  * @cong_bits: mask of WB_[a]sync_congested bits to test
  *
  * Tests whether @inode is congested.  @cong_bits is the mask of congestion
@@ -710,6 +710,9 @@ void wbc_account_io(struct writeback_con
  * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
  * associated with @inode is congested; otherwise, the root wb's congestion
  * state is used.
+ *
+ * @inode is allowed to be NULL as this function is often called on
+ * mapping->host which is NULL for the swapper space.
  */
 int inode_congested(struct inode *inode, int cong_bits)
 {

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