• Andreas Gruenbacher's avatar
    gfs2: Fix iomap write page reclaim deadlock · d0a22a4b
    Andreas Gruenbacher authored
    Since commit 64bc06bb ("gfs2: iomap buffered write support"), gfs2 is doing
    buffered writes by starting a transaction in iomap_begin, writing a range of
    pages, and ending that transaction in iomap_end.  This approach suffers from
    two problems:
    
      (1) Any allocations necessary for the write are done in iomap_begin, so when
      the data aren't journaled, there is no need for keeping the transaction open
      until iomap_end.
    
      (2) Transactions keep the gfs2 log flush lock held.  When
      iomap_file_buffered_write calls balance_dirty_pages, this can end up calling
      gfs2_write_inode, which will try to flush the log.  This requires taking the
      log flush lock which is already held, resulting in a deadlock.
    
    Fix both of these issues by not keeping transactions open from iomap_begin to
    iomap_end.  Instead, start a small transaction in page_prepare and end it in
    page_done when necessary.
    Reported-by: default avatarEdwin Török <edvin.torok@citrix.com>
    Fixes: 64bc06bb ("gfs2: iomap buffered write support")
    Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
    Signed-off-by: default avatarBob Peterson <rpeterso@redhat.com>
    d0a22a4b
bmap.c 64.8 KB