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    Btrfs: fix our reservations for updating an inode when completing io · 7fd2ae21
    Josef Bacik 提交于
    People have been reporting ENOSPC crashes in finish_ordered_io.  This is because
    we try to steal from the delalloc block rsv to satisfy a reservation to update
    the inode.  The problem with this is we don't explicitly save space for updating
    the inode when doing delalloc.  This is kind of a problem and we've gotten away
    with this because way back when we just stole from the delalloc reserve without
    any questions, and this worked out fine because generally speaking the leaf had
    been modified either by the mtime update when we did the original write or
    because we just updated the leaf when we inserted the file extent item, only on
    rare occasions had the leaf not actually been modified, and that was still ok
    because we'd just use a block or two out of the over-reservation that is
    delalloc.
    
    Then came the delayed inode stuff.  This is amazing, except it wants a full
    reservation for updating the inode since it may do it at some point down the
    road after we've written the blocks and we have to recow everything again.  This
    worked out because the delayed inode stuff just stole from the global reserve,
    that is until recently when I changed that because it caused other problems.
    
    So here we are, we're doing everything right and being screwed for it.  So take
    an extra reservation for the inode at delalloc reservation time and carry it
    through the life of the delalloc reservation.  If we need it we can steal it in
    the delayed inode stuff.  If we have already stolen it try and do a normal
    metadata reservation.  If that fails try to steal from the delalloc reservation.
    If _that_ fails we'll get a WARN_ON() so I can start thinking of a better way to
    solve this and in the meantime we'll steal from the global reserve.
    
    With this patch I ran xfstests 13 in a loop for a couple of hours and didn't see
    any problems.
    Signed-off-by: NJosef Bacik <josef@redhat.com>
    Signed-off-by: NChris Mason <chris.mason@oracle.com>
    7fd2ae21
extent-tree.c 201.0 KB