xfs: avoid memory allocation under m_peraglock in growfs code

Allocate the memory for the larger m_perag array before taking the
per-AG lock as the per-AG lock can be taken under the i_lock which
can be taken from reclaim context.

Reported by the new reclaim context tracing in lockdep.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Felix Blyakher <felixb@sgi.com>
Signed-off-by: Felix Blyakher <felixb@sgi.com>

1 files changed, 14 insertions, 6 deletions

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index cbd451bb484..2d0b3e1da9e 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -167,17 +167,25 @@ xfs_growfs_data_private(
         new = nb - mp->m_sb.sb_dblocks;
         oagcount = mp->m_sb.sb_agcount;
         if (nagcount > oagcount) {
+                void *new_perag, *old_perag;
+
                 xfs_filestream_flush(mp);
+
+                new_perag = kmem_zalloc(sizeof(xfs_perag_t) * nagcount,
+                                        KM_MAYFAIL);
+                if (!new_perag)
+                        return XFS_ERROR(ENOMEM);
+
                 down_write(&mp->m_peraglock);
-                mp->m_perag = kmem_realloc(mp->m_perag,
-                        sizeof(xfs_perag_t) * nagcount,
-                        sizeof(xfs_perag_t) * oagcount,
-                        KM_SLEEP);
-                memset(&mp->m_perag[oagcount], 0,
-                        (nagcount - oagcount) * sizeof(xfs_perag_t));
+                memcpy(new_perag, mp->m_perag, sizeof(xfs_perag_t) * oagcount);
+                old_perag = mp->m_perag;
+                mp->m_perag = new_perag;
+
                 mp->m_flags |= XFS_MOUNT_32BITINODES;
                 nagimax = xfs_initialize_perag(mp, nagcount);
                 up_write(&mp->m_peraglock);
+
+                kmem_free(old_perag);
         }
         tp = xfs_trans_alloc(mp, XFS_TRANS_GROWFS);
         tp->t_flags |= XFS_TRANS_RESERVE;