On Sat, Aug 07, 2010 at 11:09:13AM +0200, Julia Lawall wrote:
> From: Julia Lawall <julia@xxxxxxx>
>
> list_for_each_entry uses its first argument to move from one element to the
> next, so modifying it can break the iteration.
Thanks for catching the bug. It was introduced by 800deef3
[ocfs2: use list_for_each_entry where benefical]. I blame Christoph.
> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
> index 9dfaac7..7084a11 100644
> --- a/fs/ocfs2/dlm/dlmrecovery.c
> +++ b/fs/ocfs2/dlm/dlmrecovery.c
> @@ -1792,10 +1792,10 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
> for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
> tmpq = dlm_list_idx_to_ptr(res, j);
> list_for_each_entry(lock, tmpq, list) {
> - if (lock->ml.cookie != ml->cookie)
> + if (lock->ml.cookie != ml->cookie) {
> lock = NULL;
> - else
> break;
> + }
> }
> if (lock)
> break;
However, this is not the correct solution. The goal of the
original code, which used to use list_for_each(), was to leave lock
non-NULL if the cookie was found. Your version merely exits the loop on
the first non-matching entry, always leaving lock==NULL if there is a
non-matching entry.
One possible solution is to return the original code:
--8<-----------------------------------------------------------------
@@ -1747,7 +1747,7 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
struct dlm_migratable_lockres *mres)
{
struct dlm_migratable_lock *ml;
- struct list_head *queue;
+ struct list_head *queue, *iter;
struct list_head *tmpq = NULL;
struct dlm_lock *newlock = NULL;
struct dlm_lockstatus *lksb = NULL;
@@ -1791,11 +1791,12 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
spin_lock(&res->spinlock);
for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
tmpq = dlm_list_idx_to_ptr(res, j);
- list_for_each_entry(lock, tmpq, list) {
- if (lock->ml.cookie != ml->cookie)
- lock = NULL;
- else
+ list_for_each(iter, tmpq) {
+ lock = list_entry(iter, struct dlm_lock, list);
+
+ if (lock->ml.cookie == ml->cookie)
break;
+ lock = NULL;
}
if (lock)
break;
-->8-----------------------------------------------------------------
Another approach would be to keep list_for_each_entry() around,
but use a better check for entry existence:
--8<-----------------------------------------------------------------
@@ -1792,13 +1792,12 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
tmpq = dlm_list_idx_to_ptr(res, j);
list_for_each_entry(lock, tmpq, list) {
- if (lock->ml.cookie != ml->cookie)
- lock = NULL;
- else
+ if (lock->ml.cookie == ml->cookie)
break;
}
- if (lock)
+ if (&lock->list != tmpq)
break;
+ lock = NULL;
}
/* lock is always created locally first, and
-->8-----------------------------------------------------------------
I think I like the second one better. Sunil, what do you think?
Joel
--
Life's Little Instruction Book #335
"Every so often, push your luck."
Joel Becker
Consulting Software Developer
Oracle
E-mail: joel.becker@xxxxxxxxxx
Phone: (650) 506-8127
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