From: Brian Foster bfoster@redhat.com
[ Upstream commit 892a666fafa19ab04b5e948f6c92f98f1dafb489 ]
The for_each_perag*() set of macros are hacky in that some (i.e. those based on sb_agcount) rely on the assumption that perag iteration terminates naturally with a NULL perag at the specified end_agno. Others allow for the final AG to have a valid perag and require the calling function to clean up any potential leftover xfs_perag reference on termination of the loop.
Aside from providing a subtly inconsistent interface, the former variant is racy with growfs because growfs can create discoverable post-eofs perags before the final superblock update that completes the grow operation and increases sb_agcount. This leads to the following assert failure (reproduced by xfs/104) in the perag free path during unmount:
XFS: Assertion failed: atomic_read(&pag->pag_ref) == 0, file: fs/xfs/libxfs/xfs_ag.c, line: 195
This occurs because one of the many for_each_perag() loops in the code that is expected to terminate with a NULL pag (and thus has no post-loop xfs_perag_put() check) raced with a growfs and found a non-NULL post-EOFS perag, but terminated naturally based on the end_agno check without releasing the post-EOFS perag.
Rework the iteration logic to lift the agno check from the main for loop conditional to the iteration helper function. The for loop now purely terminates on a NULL pag and xfs_perag_next() avoids taking a reference to any perag beyond end_agno in the first place.
Fixes: f250eedcf762 ("xfs: make for_each_perag... a first class citizen") Signed-off-by: Brian Foster bfoster@redhat.com Reviewed-by: Dave Chinner dchinner@redhat.com Reviewed-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Leah Rumancik leah.rumancik@gmail.com Acked-by: Darrick J. Wong djwong@kernel.org --- fs/xfs/libxfs/xfs_ag.h | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h index 4585ebb3f450..3f597cad2c33 100644 --- a/fs/xfs/libxfs/xfs_ag.h +++ b/fs/xfs/libxfs/xfs_ag.h @@ -116,30 +116,26 @@ void xfs_perag_put(struct xfs_perag *pag);
/* * Perag iteration APIs - * - * XXX: for_each_perag_range() usage really needs an iterator to clean up when - * we terminate at end_agno because we may have taken a reference to the perag - * beyond end_agno. Right now callers have to be careful to catch and clean that - * up themselves. This is not necessary for the callers of for_each_perag() and - * for_each_perag_from() because they terminate at sb_agcount where there are - * no perag structures in tree beyond end_agno. */ static inline struct xfs_perag * xfs_perag_next( struct xfs_perag *pag, - xfs_agnumber_t *agno) + xfs_agnumber_t *agno, + xfs_agnumber_t end_agno) { struct xfs_mount *mp = pag->pag_mount;
*agno = pag->pag_agno + 1; xfs_perag_put(pag); + if (*agno > end_agno) + return NULL; return xfs_perag_get(mp, *agno); }
#define for_each_perag_range(mp, agno, end_agno, pag) \ for ((pag) = xfs_perag_get((mp), (agno)); \ - (pag) != NULL && (agno) <= (end_agno); \ - (pag) = xfs_perag_next((pag), &(agno))) + (pag) != NULL; \ + (pag) = xfs_perag_next((pag), &(agno), (end_agno)))
#define for_each_perag_from(mp, agno, pag) \ for_each_perag_range((mp), (agno), (mp)->m_sb.sb_agcount - 1, (pag))