Messages in this thread | | | Date | Tue, 22 Mar 2022 10:15:34 +0800 | Subject | Re: [PATCH] ocfs2: fix check if list iterator did find an element | From | Joseph Qi <> |
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On 3/21/22 9:34 PM, Jakob Koschel wrote: > >> On 21. Mar 2022, at 02:50, Joseph Qi <joseph.qi@linux.alibaba.com> wrote: >> >> >> >> On 3/20/22 4:31 AM, Jakob Koschel wrote: >>> Instead of setting 'res' to NULL, it should only be set if >>> the suitable element was found. >>> >>> In the original code 'res' would have been set to an incorrect pointer >>> if the list is empty. >>> >> The logic before iteration can make sure track_list won't be empty. >> Please refer the discussion via: >> https://lore.kernel.org/ocfs2-devel/bd0ec87e-b490-83dc-2363-5e5342c59fa4@linux.alibaba.com/T/#m96d4397930201d83d68677c33a9721ae8dbd8f15 > > ah yes, I just read up on the discussion there, sorry for having duplicated it > here. > > Was any conclusion reached there which fixes can/should be merged? > > This code obviously can always be safe if the list cannot be empty. > That's also not necessarily the reason I'm fixing this. The reason is that > we want to get rid of any use of the list iterator variable after the loop > ('res' in this case). This will allow moving the list iterator variable > into the scope of the list iterator macro to forbid any invalid use of it > at compile time. Like this you don't have to rely on assumptions that are > hard to validate (e.g. that a certain list is never empty). > > The patch here is the minimal change to simply do that but looking at > Dan Carpenter patch there might be more things in this code that can > be simplified. > Agree, so I'm fine with this change. So could you please update the description and send v2?
Thanks, Joseph
> [CC'd Dan Carpenter] > > See [1] for changes that have already been merged: > > [1] https://lore.kernel.org/linux-kernel/20220308171818.384491-3-jakobkoschel@gmail.com/ > >> >> Thanks, >> Joseph >> >>> In preparation to limit the scope of the list iterator to the list >>> traversal loop, use a dedicated pointer pointing to the found element [1]. >>> >>> Link: https://lore.kernel.org/all/YhdfEIwI4EdtHdym@kroah.com/ >>> Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com> >>> --- >>> fs/ocfs2/dlm/dlmdebug.c | 12 ++++++------ >>> 1 file changed, 6 insertions(+), 6 deletions(-) >>> >>> diff --git a/fs/ocfs2/dlm/dlmdebug.c b/fs/ocfs2/dlm/dlmdebug.c >>> index d442cf5dda8a..be5e9ed7da8d 100644 >>> --- a/fs/ocfs2/dlm/dlmdebug.c >>> +++ b/fs/ocfs2/dlm/dlmdebug.c >>> @@ -541,7 +541,7 @@ static void *lockres_seq_start(struct seq_file *m, loff_t *pos) >>> struct debug_lockres *dl = m->private; >>> struct dlm_ctxt *dlm = dl->dl_ctxt; >>> struct dlm_lock_resource *oldres = dl->dl_res; >>> - struct dlm_lock_resource *res = NULL; >>> + struct dlm_lock_resource *res = NULL, *iter; >>> struct list_head *track_list; >>> >>> spin_lock(&dlm->track_lock); >>> @@ -556,11 +556,11 @@ static void *lockres_seq_start(struct seq_file *m, loff_t *pos) >>> } >>> } >>> >>> - list_for_each_entry(res, track_list, tracking) { >>> - if (&res->tracking == &dlm->tracking_list) >>> - res = NULL; >>> - else >>> - dlm_lockres_get(res); >>> + list_for_each_entry(iter, track_list, tracking) { >>> + if (&iter->tracking != &dlm->tracking_list) { >>> + dlm_lockres_get(iter); >>> + res = iter; >>> + } >>> break; >>> } >>> spin_unlock(&dlm->track_lock); >>> >>> base-commit: 34e047aa16c0123bbae8e2f6df33e5ecc1f56601 >>> -- >>> 2.25.1 > > Jakob
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