Commit 8aea3ff4 authored Sep 20, 2012 by Carlos Maiolino Committed by Ben Myers Sep 26, 2012

xfs: Fix m_agirotor reset during AG selection



xfs_ialloc_next_ag() currently resets m_agirotor when it is equal to
m_maxagi:

         if (++mp->m_agirotor == mp->m_maxagi)
	         mp->m_agirotor = 0;

But, if for some reason mp->m_maxagi changes to a lower value than
current m_agirotor, this condition will never be true, causing
m_agirotor to exceed the maximum allowed value (m_maxagi).

This implies mainly during lookups for xfs_perag structs in its radix
tree, since the agno value used for the lookup is based on m_agirotor.
An out-of-range m_agirotor may cause a lookup failure which in case will
return NULL.

As an example, the value of m_maxagi is decreased during
inode64->inode32 remount process, case where I've found this problem.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

parent c3a58fec

fs/xfs/xfs_ialloc.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -431,7 +431,7 @@ xfs_ialloc_next_ag(

		spin_lock(&mp->m_agirotor_lock);
		agno = mp->m_agirotor;
		if (++mp->m_agirotor == mp->m_maxagi)
		if (++mp->m_agirotor >= mp->m_maxagi)
		mp->m_agirotor = 0;
		spin_unlock(&mp->m_agirotor_lock);

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