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SubjectRe: Oops: Quota race in 2.4.12?
  Hi,

> Some of our dual CPU web servers with 2.4.12 are Oopsing while running
> quotacheck. They don't seem to die immediately, but oops many times and
> eventually break. The old tools didn't warn about quotachecking on a
> live file system, so some of our servers were set up to run quotacheck
> nightly. The new tools still allow you to do it, but warn that it may
> not be consistent. We didn't have any problems with 2.2 kernels.
>
> First oops, as already processed (grumble) by klogd:
>
> Oct 28 04:22:32 pro kernel: remove_free_dquot: dquot not on the free list??
> Oct 28 04:22:32 pro last message repeated 90 times
> Oct 28 04:22:32 pro kernel: Unable to handle kernel NULL pointer dereference at virtual address 00000004
> ...dates stripped:
<snip>

Attached is the patch against 2.4.13 which should solve some SMP races... Can you try
it if it fixes your problems? I know also about one possible race during quotaoff()
which I'll fix tonight but that shouldn't be your case :).
Honza
diff -ruX /home/jack/.kerndiffexclude linux-2.4.13/fs/dquot.c linux-2.4.13-locksfix/fs/dquot.c
--- linux-2.4.13/fs/dquot.c Thu Oct 11 00:08:48 2001
+++ linux-2.4.13-locksfix/fs/dquot.c Wed Oct 31 00:20:17 2001
@@ -330,24 +330,6 @@
unlock_dquot(dquot);
}

-/*
- * Unhash and selectively clear the dquot structure,
- * but preserve the use count, list pointers, and
- * wait queue.
- */
-void clear_dquot(struct dquot *dquot)
-{
- /* unhash it first */
- remove_dquot_hash(dquot);
- dquot->dq_sb = NULL;
- dquot->dq_id = 0;
- dquot->dq_dev = NODEV;
- dquot->dq_type = -1;
- dquot->dq_flags = 0;
- dquot->dq_referenced = 0;
- memset(&dquot->dq_dqb, 0, sizeof(struct dqblk));
-}
-
/* Invalidate all dquots on the list, wait for all users. Note that this function is called
* after quota is disabled so no new quota might be created. As we only insert to the end of
* inuse list, we don't have to restart searching... */
@@ -384,6 +366,7 @@
struct list_head *head;
struct dquot *dquot;

+ lock_kernel();
restart:
for (head = inuse_list.next; head != &inuse_list; head = head->next) {
dquot = list_entry(head, struct dquot, dq_inuse);
@@ -405,6 +388,7 @@
goto restart;
}
dqstats.syncs++;
+ unlock_kernel();
return 0;
}

@@ -428,7 +412,9 @@

int shrink_dqcache_memory(int priority, unsigned int gfp_mask)
{
+ lock_kernel();
prune_dqcache(nr_free_dquots / (priority + 1));
+ unlock_kernel();
kmem_cache_shrink(dquot_cachep);
return 0;
}
@@ -470,7 +456,7 @@
wake_up(&dquot->dq_wait_free);
}

-struct dquot *get_empty_dquot(void)
+static struct dquot *get_empty_dquot(void)
{
struct dquot *dquot;

@@ -633,9 +619,11 @@
/* Free list of dquots - called from inode.c */
void put_dquot_list(struct list_head *tofree_head)
{
- struct list_head *act_head = tofree_head->next;
+ struct list_head *act_head;
struct dquot *dquot;

+ lock_kernel();
+ act_head = tofree_head->next;
/* So now we have dquots on the list... Just free them */
while (act_head != tofree_head) {
dquot = list_entry(act_head, struct dquot, dq_free);
@@ -644,6 +632,7 @@
INIT_LIST_HEAD(&dquot->dq_free);
dqput(dquot);
}
+ unlock_kernel();
}

static inline void dquot_incr_inodes(struct dquot *dquot, unsigned long number)
@@ -1289,6 +1278,7 @@
short cnt;
struct quota_mount_options *dqopt = sb_dqopt(sb);

+ lock_kernel();
if (!sb)
goto out;

@@ -1313,6 +1303,7 @@
}
up(&dqopt->dqoff_sem);
out:
+ unlock_kernel();
return 0;
}

diff -ruX /home/jack/.kerndiffexclude linux-2.4.13/fs/inode.c linux-2.4.13-locksfix/fs/inode.c
--- linux-2.4.13/fs/inode.c Tue Oct 30 22:54:35 2001
+++ linux-2.4.13-locksfix/fs/inode.c Tue Oct 30 22:56:18 2001
@@ -1210,9 +1210,9 @@

if (!sb->dq_op)
return; /* nothing to do */
-
/* We have to be protected against other CPUs */
- spin_lock(&inode_lock);
+ lock_kernel(); /* This lock is for quota code */
+ spin_lock(&inode_lock); /* This lock is for inodes code */

list_for_each(act_head, &inode_in_use) {
inode = list_entry(act_head, struct inode, i_list);
@@ -1235,6 +1235,7 @@
remove_inode_dquot_ref(inode, type, &tofree_head);
}
spin_unlock(&inode_lock);
+ unlock_kernel();

put_dquot_list(&tofree_head);
}
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