• Darrick J. Wong's avatar
    xfs: fix deadlock and streamline xfs_getfsmap performance · 8ffa90e1
    Darrick J. Wong authored
    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: 4c934c7d ("xfs: report realtime space information via the rtbitmap")
    Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Reviewed-by: default avatarChandan Babu R <chandanrlinux@gmail.com>
    8ffa90e1
xfs_fsmap.c 25.5 KB