tree c4bb565a5a71bd95ebd9802d4caead64ae7146d1
parent 91d1d3d97e3316d0bd43cdce7cfa9171c687ebf5
author Darrick J. Wong <darrick.wong@oracle.com> 1601574967 -0700
committer Darrick J. Wong <darrick.wong@oracle.com> 1601917880 -0700

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>