From 09d967c6f32b35eab15b45862ae16e4f06259d8e Mon Sep 17 00:00:00 2001
From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Date: Thu, 22 Jun 2006 14:47:21 -0700
Subject: [PATCH] [PATCH] Fix a race condition between ->i_mapping and iput()
This race became a cause of oops, and can reproduce by the following.
while true; do
dd if=/dev/zero of=/dev/.static/dev/hdg1 bs=512 count=1000 & sync
done
This race condition was between __sync_single_inode() and iput().
cpu0 (fs's inode) cpu1 (bdev's inode)
----------------- -------------------
close("/dev/hda2")
[...]
__sync_single_inode()
/* copy the bdev's ->i_mapping */
mapping = inode->i_mapping;
generic_forget_inode()
bdev_clear_inode()
/* restre the fs's ->i_mapping */
inode->i_mapping = &inode->i_data;
/* bdev's inode was freed */
destroy_inode(inode);
if (wait) {
/* dereference a freed bdev's mapping->host */
filemap_fdatawait(mapping); /* Oops */
Since __sync_single_inode() is only taking a ref-count of fs's inode, the
another process can be close() and freeing the bdev's inode while writing
fs's inode. So, __sync_signle_inode() accesses the freed ->i_mapping,
oops.
This patch takes a ref-count on the bdev's inode for the fs's inode before
setting a ->i_mapping, and the clear_inode() of the fs's inode does iput() on
the bdev's inode. So if the fs's inode is still living, bdev's inode
shouldn't be freed.
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
fs/block_dev.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index f5958f413bd1..44aaba202f78 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -414,21 +414,31 @@ EXPORT_SYMBOL(bdput);
static struct block_device *bd_acquire(struct inode *inode)
{
struct block_device *bdev;
+
spin_lock(&bdev_lock);
bdev = inode->i_bdev;
- if (bdev && igrab(bdev->bd_inode)) {
+ if (bdev) {
+ atomic_inc(&bdev->bd_inode->i_count);
spin_unlock(&bdev_lock);
return bdev;
}
spin_unlock(&bdev_lock);
+
bdev = bdget(inode->i_rdev);
if (bdev) {
spin_lock(&bdev_lock);
- if (inode->i_bdev)
- __bd_forget(inode);
- inode->i_bdev = bdev;
- inode->i_mapping = bdev->bd_inode->i_mapping;
- list_add(&inode->i_devices, &bdev->bd_inodes);
+ if (!inode->i_bdev) {
+ /*
+ * We take an additional bd_inode->i_count for inode,
+ * and it's released in clear_inode() of inode.
+ * So, we can access it via ->i_mapping always
+ * without igrab().
+ */
+ atomic_inc(&bdev->bd_inode->i_count);
+ inode->i_bdev = bdev;
+ inode->i_mapping = bdev->bd_inode->i_mapping;
+ list_add(&inode->i_devices, &bdev->bd_inodes);
+ }
spin_unlock(&bdev_lock);
}
return bdev;
@@ -438,10 +448,18 @@ static struct block_device *bd_acquire(struct inode *inode)
void bd_forget(struct inode *inode)
{
+ struct block_device *bdev = NULL;
+
spin_lock(&bdev_lock);
- if (inode->i_bdev)
+ if (inode->i_bdev) {
+ if (inode->i_sb != blockdev_superblock)
+ bdev = inode->i_bdev;
__bd_forget(inode);
+ }
spin_unlock(&bdev_lock);
+
+ if (bdev)
+ iput(bdev->bd_inode);
}
int bd_claim(struct block_device *bdev, void *holder)
--
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