xfs: fix deadlock and streamline xfs_getfsmap performance

Refactor xfs_getfsmap to improve its performance: instead of indirectly
calling a function that copies one record to userspace at a time, create
a shadow buffer in the kernel and copy the whole array once at the end.
On the author's computer, this reduces the runtime on his /home by ~20%.

This also eliminates a deadlock when running GETFSMAP against the
realtime device.  The current code locks the rtbitmap to create
fsmappings and copies them into userspace, having not released the
rtbitmap lock.  If the userspace buffer is an mmap of a sparse file that
itself resides on the realtime device, the write page fault will recurse
into the fs for allocation, which will deadlock on the rtbitmap lock.

Fixes: 4c934c7dd60c ("xfs: report realtime space information via the rtbitmap")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>

1 files changed, 1 insertions, 5 deletions

diff --git a/fs/xfs/xfs_fsmap.h b/fs/xfs/xfs_fsmap.h
index c6c57739b862..a0775788e7b1 100644
--- a/fs/xfs/xfs_fsmap.h
+++ b/fs/xfs/xfs_fsmap.h
@@ -27,13 +27,9 @@ struct xfs_fsmap_head {
 	struct xfs_fsmap fmh_keys[2];	/* low and high keys */
 };
 
-void xfs_fsmap_from_internal(struct fsmap *dest, struct xfs_fsmap *src);
 void xfs_fsmap_to_internal(struct xfs_fsmap *dest, struct fsmap *src);
 
-/* fsmap to userspace formatter - copy to user & advance pointer */
-typedef int (*xfs_fsmap_format_t)(struct xfs_fsmap *, void *);
-
 int xfs_getfsmap(struct xfs_mount *mp, struct xfs_fsmap_head *head,
-		xfs_fsmap_format_t formatter, void *arg);
+		struct fsmap *out_recs);
 
 #endif /* __XFS_FSMAP_H__ */