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Btrfs: fix page->private races

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There is a race where btrfs_releasepage can drop the
page->private contents just as alloc_extent_buffer is setting
up pages for metadata.  Because of how the Btrfs page flags work,
this results in us skipping the crc on the page during IO.

This patch sovles the race by waiting until after the extent buffer
is inserted into the radix tree before it sets page private.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason 2011-02-10 12:35:00 -05:00
parent 3a90983dbd
commit eb14ab8ed2
2 changed files with 41 additions and 5 deletions
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8
fs/btrfs/disk-io.c
View File

@ -359,10 +359,14 @@ static int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
tree = &BTRFS_I(page->mapping->host)->io_tree; tree = &BTRFS_I(page->mapping->host)->io_tree;
if (page->private == EXTENT_PAGE_PRIVATE) if (page->private == EXTENT_PAGE_PRIVATE) {
WARN_ON(1);
goto out; goto out;
if (!page->private) }
if (!page->private) {
WARN_ON(1);
goto out; goto out;
}
len = page->private >> 2; len = page->private >> 2;
WARN_ON(len == 0); WARN_ON(len == 0);

36
fs/btrfs/extent_io.c
View File

@ -1946,6 +1946,7 @@ void set_page_extent_mapped(struct page *page)
static void set_page_extent_head(struct page *page, unsigned long len) static void set_page_extent_head(struct page *page, unsigned long len)
{ {
WARN_ON(!PagePrivate(page));
set_page_private(page, EXTENT_PAGE_PRIVATE_FIRST_PAGE | len << 2); set_page_private(page, EXTENT_PAGE_PRIVATE_FIRST_PAGE | len << 2);
} }
@ -3195,6 +3196,12 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
} }
if (!PageUptodate(p)) if (!PageUptodate(p))
uptodate = 0; uptodate = 0;
/*
* see below about how we avoid a nasty race with release page
* and why we unlock later
*/
if (i != 0)
unlock_page(p); unlock_page(p);
} }
if (uptodate) if (uptodate)
@ -3219,9 +3226,26 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
atomic_inc(&eb->refs); atomic_inc(&eb->refs);
spin_unlock(&tree->buffer_lock); spin_unlock(&tree->buffer_lock);
radix_tree_preload_end(); radix_tree_preload_end();
/*
* there is a race where release page may have
* tried to find this extent buffer in the radix
* but failed. It will tell the VM it is safe to
* reclaim the, and it will clear the page private bit.
* We must make sure to set the page private bit properly
* after the extent buffer is in the radix tree so
* it doesn't get lost
*/
set_page_extent_mapped(eb->first_page);
set_page_extent_head(eb->first_page, eb->len);
if (!page0)
unlock_page(eb->first_page);
return eb; return eb;
free_eb: free_eb:
if (eb->first_page && !page0)
unlock_page(eb->first_page);
if (!atomic_dec_and_test(&eb->refs)) if (!atomic_dec_and_test(&eb->refs))
return exists; return exists;
btrfs_release_extent_buffer(eb); btrfs_release_extent_buffer(eb);
@ -3272,10 +3296,11 @@ int clear_extent_buffer_dirty(struct extent_io_tree *tree,
continue; continue;
lock_page(page); lock_page(page);
WARN_ON(!PagePrivate(page));
set_page_extent_mapped(page);
if (i == 0) if (i == 0)
set_page_extent_head(page, eb->len); set_page_extent_head(page, eb->len);
else
set_page_private(page, EXTENT_PAGE_PRIVATE);
clear_page_dirty_for_io(page); clear_page_dirty_for_io(page);
spin_lock_irq(&page->mapping->tree_lock); spin_lock_irq(&page->mapping->tree_lock);
@ -3465,6 +3490,13 @@ int read_extent_buffer_pages(struct extent_io_tree *tree,
for (i = start_i; i < num_pages; i++) { for (i = start_i; i < num_pages; i++) {
page = extent_buffer_page(eb, i); page = extent_buffer_page(eb, i);
WARN_ON(!PagePrivate(page));
set_page_extent_mapped(page);
if (i == 0)
set_page_extent_head(page, eb->len);
if (inc_all_pages) if (inc_all_pages)
page_cache_get(page); page_cache_get(page);
if (!PageUptodate(page)) { if (!PageUptodate(page)) {