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pNFS: Fix a deadlock when coalescing writes and returning the layout
Consider the following deadlock: Process P1 Process P2 Process P3 ========== ========== ========== lock_page(page) lseg = pnfs_update_layout(inode) lo = NFS_I(inode)->layout pnfs_error_mark_layout_for_return(lo) lock_page(page) lseg = pnfs_update_layout(inode) In this scenario, - P1 has declared the layout to be in error, but P2 holds a reference to a layout segment on that inode, so the layoutreturn is deferred. - P2 is waiting for a page lock held by P3. - P3 is asking for a new layout segment, but is blocked waiting for the layoutreturn. The fix is to ensure that pnfs_error_mark_layout_for_return() does not set the NFS_LAYOUT_RETURN flag, which blocks P3. Instead, we allow the latter to call LAYOUTGET so that it can make progress and unblock P2. Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
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@ -2063,8 +2063,6 @@ void pnfs_error_mark_layout_for_return(struct inode *inode,
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return;
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}
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pnfs_set_plh_return_info(lo, range.iomode, 0);
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/* Block LAYOUTGET */
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set_bit(NFS_LAYOUT_RETURN, &lo->plh_flags);
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/*
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* mark all matching lsegs so that we are sure to have no live
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* segments at hand when sending layoutreturn. See pnfs_put_lseg()
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