Allocating pagecache pages within the disk request_fn is deadlocky and prone
to page allocation failures, causing write I/O errors.
Attempt to bandaid things up.
---
25-akpm/drivers/block/rd.c | 31 ++++++++++++++++++++++++++-----
1 files changed, 26 insertions(+), 5 deletions(-)
diff -puN drivers/block/rd.c~ramdisk-memory-allocation-fixes drivers/block/rd.c
--- 25/drivers/block/rd.c~ramdisk-memory-allocation-fixes 2004-05-17 22:11:30.352130848 -0700
+++ 25-akpm/drivers/block/rd.c 2004-05-17 22:11:30.356130240 -0700
@@ -320,18 +320,39 @@ static int rd_open(struct inode *inode,
{
unsigned unit = iminor(inode);
- /*
- * Immunize device against invalidate_buffers() and prune_icache().
- */
if (rd_bdev[unit] == NULL) {
struct block_device *bdev = inode->i_bdev;
+ struct address_space *mapping;
+ int gfp_mask;
+
inode = igrab(bdev->bd_inode);
rd_bdev[unit] = bdev;
bdev->bd_openers++;
bdev->bd_block_size = rd_blocksize;
inode->i_size = get_capacity(rd_disks[unit])<<9;
- inode->i_mapping->a_ops = &ramdisk_aops;
- inode->i_mapping->backing_dev_info = &rd_backing_dev_info;
+ mapping = inode->i_mapping;
+ mapping->a_ops = &ramdisk_aops;
+ mapping->backing_dev_info = &rd_backing_dev_info;
+
+ /*
+ * Deep badness. rd_blkdev_pagecache_IO() needs to allocate
+ * pagecache pages within a request_fn. We cannot recur back
+ * into the filesytem which is mounted atop the ramdisk, because
+ * that would deadlock on fs locks. And we really don't want
+ * to reenter rd_blkdev_pagecache_IO when we're already within
+ * that function.
+ *
+ * So we turn off __GFP_FS and __GFP_IO.
+ *
+ * And to give this thing a hope of working, turn on __GFP_HIGH.
+ * Hopefully, there's enough regular memory allocation going on
+ * for the page allocator emergency pools to keep the ramdisk
+ * driver happy.
+ */
+ gfp_mask = mapping_gfp_mask(mapping);
+ gfp_mask &= ~(__GFP_FS|__GFP_IO);
+ gfp_mask |= __GFP_HIGH;
+ mapping_set_gfp_mask(mapping, gfp_mask);
}
return 0;
_