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authorChristoph Hellwig <hch@infradead.org>2010-07-20 17:31:01 +1000
committerAlex Elder <aelder@sgi.com>2010-07-26 13:16:51 -0500
commit0664ce8d0fde731d76fa7e86b3afb54f3a6830ff (patch)
treec33c78d3a3e34ecc7f1ddda363040b57687b6b25 /fs/xfs/xfs_filestream.c
parent73523a2ecf03f0bfe7c36c244aff8a2ef2208a4a (diff)
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xfs: clean up filestreams helpers
Move xfs_filestream_peek_ag, xxfs_filestream_get_ag and xfs_filestream_put_ag from xfs_filestream.h to xfs_filestream.c where it's only callers are, and remove the inline marker while we're at it to let the compiler decide on the inlining. Also don't return a value from xfs_filestream_put_ag because we don't need it. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
Diffstat (limited to 'fs/xfs/xfs_filestream.c')
-rw-r--r--fs/xfs/xfs_filestream.c80
1 files changed, 77 insertions, 3 deletions
diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
index d34b9e8d2d3..9b715dce569 100644
--- a/fs/xfs/xfs_filestream.c
+++ b/fs/xfs/xfs_filestream.c
@@ -123,6 +123,82 @@ typedef struct fstrm_item
xfs_inode_t *pip; /* Parent directory inode pointer. */
} fstrm_item_t;
+/*
+ * Allocation group filestream associations are tracked with per-ag atomic
+ * counters. These counters allow _xfs_filestream_pick_ag() to tell whether a
+ * particular AG already has active filestreams associated with it. The mount
+ * point's m_peraglock is used to protect these counters from per-ag array
+ * re-allocation during a growfs operation. When xfs_growfs_data_private() is
+ * about to reallocate the array, it calls xfs_filestream_flush() with the
+ * m_peraglock held in write mode.
+ *
+ * Since xfs_mru_cache_flush() guarantees that all the free functions for all
+ * the cache elements have finished executing before it returns, it's safe for
+ * the free functions to use the atomic counters without m_peraglock protection.
+ * This allows the implementation of xfs_fstrm_free_func() to be agnostic about
+ * whether it was called with the m_peraglock held in read mode, write mode or
+ * not held at all. The race condition this addresses is the following:
+ *
+ * - The work queue scheduler fires and pulls a filestream directory cache
+ * element off the LRU end of the cache for deletion, then gets pre-empted.
+ * - A growfs operation grabs the m_peraglock in write mode, flushes all the
+ * remaining items from the cache and reallocates the mount point's per-ag
+ * array, resetting all the counters to zero.
+ * - The work queue thread resumes and calls the free function for the element
+ * it started cleaning up earlier. In the process it decrements the
+ * filestreams counter for an AG that now has no references.
+ *
+ * With a shrinkfs feature, the above scenario could panic the system.
+ *
+ * All other uses of the following macros should be protected by either the
+ * m_peraglock held in read mode, or the cache's internal locking exposed by the
+ * interval between a call to xfs_mru_cache_lookup() and a call to
+ * xfs_mru_cache_done(). In addition, the m_peraglock must be held in read mode
+ * when new elements are added to the cache.
+ *
+ * Combined, these locking rules ensure that no associations will ever exist in
+ * the cache that reference per-ag array elements that have since been
+ * reallocated.
+ */
+static int
+xfs_filestream_peek_ag(
+ xfs_mount_t *mp,
+ xfs_agnumber_t agno)
+{
+ struct xfs_perag *pag;
+ int ret;
+
+ pag = xfs_perag_get(mp, agno);
+ ret = atomic_read(&pag->pagf_fstrms);
+ xfs_perag_put(pag);
+ return ret;
+}
+
+static int
+xfs_filestream_get_ag(
+ xfs_mount_t *mp,
+ xfs_agnumber_t agno)
+{
+ struct xfs_perag *pag;
+ int ret;
+
+ pag = xfs_perag_get(mp, agno);
+ ret = atomic_inc_return(&pag->pagf_fstrms);
+ xfs_perag_put(pag);
+ return ret;
+}
+
+static void
+xfs_filestream_put_ag(
+ xfs_mount_t *mp,
+ xfs_agnumber_t agno)
+{
+ struct xfs_perag *pag;
+
+ pag = xfs_perag_get(mp, agno);
+ atomic_dec(&pag->pagf_fstrms);
+ xfs_perag_put(pag);
+}
/*
* Scan the AGs starting at startag looking for an AG that isn't in use and has
@@ -351,16 +427,14 @@ xfs_fstrm_free_func(
{
fstrm_item_t *item = (fstrm_item_t *)data;
xfs_inode_t *ip = item->ip;
- int ref;
ASSERT(ip->i_ino == ino);
xfs_iflags_clear(ip, XFS_IFILESTREAM);
/* Drop the reference taken on the AG when the item was added. */
- ref = xfs_filestream_put_ag(ip->i_mount, item->ag);
+ xfs_filestream_put_ag(ip->i_mount, item->ag);
- ASSERT(ref >= 0);
TRACE_FREE(ip->i_mount, ip, item->pip, item->ag,
xfs_filestream_peek_ag(ip->i_mount, item->ag));