Commit a3b8d92d authored Dec 07, 2009 by Mel Gorman Committed by Jens Axboe Dec 09, 2009

block,xd: Delay allocation of DMA buffers until device is known



Loading the XD module triggers a warning like

 WARNING: at mm/page_alloc.c:1805
 __alloc_pages_nodemask+0x127/0x48f()
 Hardware name: System Product Name
 Modules linked in:
 Pid: 1, comm: swapper Not tainted 2.6.32-rc8-git5 #1
 Call Trace:
  [<c103d94b>] warn_slowpath_common+0x65/0x95
  [<c103d98d>] warn_slowpath_null+0x12/0x15
  [<c109550c>] __alloc_pages_nodemask+0x127/0x48f
  [<c10be964>] ? get_slab+0x8/0x50
  [<c10b8979>] alloc_page_interleave+0x2e/0x6e
  [<c10b8a10>] alloc_pages_current+0x57/0x99
  [<c2083a4a>] ? xd_init+0x0/0x482
  [<c1094c38>] __get_free_pages+0xd/0x1e
  [<c2083a94>] xd_init+0x4a/0x482
  [<c2082df0>] ? loop_init+0x104/0x16a
  [<c169162d>] ? loop_probe+0x0/0xaf
  [<c2083a4a>] ? xd_init+0x0/0x482
  [<c1001143>] do_one_initcall+0x51/0x13f
  [<c204a307>] kernel_init+0x10b/0x15f
  [<c204a1fc>] ? kernel_init+0x0/0x15f
  [<c1004347>] kernel_thread_helper+0x7/0x10
 ---[ end trace 686db6333ade6e7a ]---
 xd: Out of memory.

The warning is because the alloc_pages is called with an
order >= MAX_ORDER. The simplistic reason is that get_order(0) returns garbage
values when given 0 as a size. The more complex reason is that the XD driver
initialisation is broken.

It's not clear why this ever worked. XD allocates a buffer for DMA based
on the value of xd_maxsectors. This value is determined by the exact
type of controller in use but the value is determined *after* an attempt
has been made to allocate the buffer. i.e. the requested size of the DMA
buffer will always be 0.

This patch alters how XD is initialised slightly by allocating the
buffer when and if a device has actually been detected. The error paths
are updated to suit the new logic.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

parent 8b43aebd

drivers/block/xd.c

+19 −11

Original line number	Diff line number	Diff line
		@@ -169,13 +169,6 @@ static int __init xd_init(void)

		init_timer (&xd_watchdog_int); xd_watchdog_int.function = xd_watchdog;

		if (!xd_dma_buffer)
		xd_dma_buffer = (char )xd_dma_mem_alloc(xd_maxsectors 0x200);
		if (!xd_dma_buffer) {
		printk(KERN_ERR "xd: Out of memory.\n");
		return -ENOMEM;
		}

		err = -EBUSY;
		if (register_blkdev(XT_DISK_MAJOR, "xd"))
		goto out1;
		@@ -202,6 +195,19 @@ static int __init xd_init(void)
		xd_drives,xd_drives == 1 ? "" : "s",xd_irq,xd_dma);
		}

		/*
		* With the drive detected, xd_maxsectors should now be known.
		* If xd_maxsectors is 0, nothing was detected and we fall through
		* to return -ENODEV
		*/
		if (!xd_dma_buffer && xd_maxsectors) {
		xd_dma_buffer = (char )xd_dma_mem_alloc(xd_maxsectors 0x200);
		if (!xd_dma_buffer) {
		printk(KERN_ERR "xd: Out of memory.\n");
		goto out3;
		}
		}

		err = -ENODEV;
		if (!xd_drives)
		goto out3;
		@@ -249,15 +255,17 @@ out4:
		for (i = 0; i < xd_drives; i++)
		put_disk(xd_gendisk[i]);
		out3:
		if (xd_maxsectors)
		release_region(xd_iobase,4);

		if (xd_dma_buffer)
		xd_dma_mem_free((unsigned long)xd_dma_buffer,
		xd_maxsectors * 0x200);
		out2:
		blk_cleanup_queue(xd_queue);
		out1a:
		unregister_blkdev(XT_DISK_MAJOR, "xd");
		out1:
		if (xd_dma_buffer)
		xd_dma_mem_free((unsigned long)xd_dma_buffer,
		xd_maxsectors * 0x200);
		return err;
		Enomem:
		err = -ENOMEM;

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