xfs: switch to NOFS allocation under i_lock in xfs_buf_associate_memory

xfs_buf_associate_memory is used for setting up the spare buffer for the
log wrap case in xlog_sync which can happen under i_lock when called from
xfs_fsync. The i_lock mutex is taken in reclaim context so all allocations
under it must avoid recursions into the filesystem. There are a couple
more uses of xfs_buf_associate_memory in the log recovery code that are
also affected by this, but I'd rather keep the code simple than passing on
a gfp_mask argument. Longer term we should just stop requiring the memoery
allocation in xlog_sync by some smaller rework of the buffer layer.

Reported by the new reclaim context tracing in lockdep.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Felix Blyakher <[e-mail]>
Signed-off-by: Felix Blyakher <[e-mail]>

fs/xfs/linux-2.6/xfs_buf.c

···
 	bp->b_pages = NULL;
 	bp->b_addr = mem;
 
-	rval = _xfs_buf_get_pages(bp, page_count, 0);
+	rval = _xfs_buf_get_pages(bp, page_count, XBF_DONT_BLOCK);
 	if (rval)
 		return rval;