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Date: Wed, 25 Oct 2017 15:07:49 +0300
From: Amir Goldstein <amir73il@...il.com>
To: Miklos Szeredi <mszeredi@...hat.com>
Cc: linux-fsdevel <linux-fsdevel@...r.kernel.org>,
Jan Kara <jack@...e.cz>, Xiong Zhou <xzhou@...hat.com>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/7] fsnotify: clean up fsnotify_prepare/finish_user_wait()
On Wed, Oct 25, 2017 at 3:06 PM, Amir Goldstein <amir73il@...il.com> wrote:
> On Wed, Oct 25, 2017 at 11:41 AM, Miklos Szeredi <mszeredi@...hat.com> wrote:
>> This patch doesn't actually fix any bug, just paves the way for fixing mark
>> and group pinning.
>>
>> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
>> Cc: <stable@...r.kernel.org> # v4.12
>> ---
>> fs/notify/mark.c | 89 ++++++++++++++++++++++++++------------------------------
>> 1 file changed, 41 insertions(+), 48 deletions(-)
>>
>> diff --git a/fs/notify/mark.c b/fs/notify/mark.c
>> index 9991f8826734..982527ce6a58 100644
>> --- a/fs/notify/mark.c
>> +++ b/fs/notify/mark.c
>> @@ -109,16 +109,6 @@ void fsnotify_get_mark(struct fsnotify_mark *mark)
>> atomic_inc(&mark->refcnt);
>> }
>>
>> -/*
>> - * Get mark reference when we found the mark via lockless traversal of object
>> - * list. Mark can be already removed from the list by now and on its way to be
>> - * destroyed once SRCU period ends.
>> - */
>> -static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
>> -{
>> - return atomic_inc_not_zero(&mark->refcnt);
>> -}
>> -
>> static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
>> {
>> u32 new_mask = 0;
>> @@ -256,32 +246,56 @@ void fsnotify_put_mark(struct fsnotify_mark *mark)
>> FSNOTIFY_REAPER_DELAY);
>> }
>>
>> -bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
>> +/*
>> + * Get mark reference when we found the mark via lockless traversal of object
>> + * list. Mark can be already removed from the list by now and on its way to be
>> + * destroyed once SRCU period ends.
>> + */
>> +static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
Sorry, hit send too soon...
This helper is now more than "get mark safe"
how about fsnotify_get_mark_wait() to pair with fsnotify_put_mark_wait()?
>> {
>> struct fsnotify_group *group;
>>
>> - if (WARN_ON_ONCE(!iter_info->inode_mark && !iter_info->vfsmount_mark))
>> - return false;
>> -
>> - if (iter_info->inode_mark)
>> - group = iter_info->inode_mark->group;
>> - else
>> - group = iter_info->vfsmount_mark->group;
>> + if (!mark)
>> + return true;
>>
>> + group = mark->group;
>> /*
>> * Since acquisition of mark reference is an atomic op as well, we can
>> * be sure this inc is seen before any effect of refcount increment.
>> */
>> atomic_inc(&group->user_waits);
>> + if (atomic_inc_not_zero(&mark->refcnt))
>> + return true;
>> +
>
> Please replicate the "We abuse notification_waitq on group shutdown" comment
> here as well to clarify why this wakeup is needed. Although comment says
> "for waiting for all marks pinned" and this code path did not change
> mark refcount,
> so is the wakeup really needed here?
>
>> + if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
>> + wake_up(&group->notification_waitq);
>>
>> - if (iter_info->inode_mark) {
>> - /* This can fail if mark is being removed */
>> - if (!fsnotify_get_mark_safe(iter_info->inode_mark))
>> - goto out_wait;
>> + return false;
>> +}
>> +
>> +static void fsnotify_put_mark_wait(struct fsnotify_mark *mark)
>> +{
>> + if (mark) {
>> + struct fsnotify_group *group = mark->group;
>> +
>> + fsnotify_put_mark(mark);
>> + /*
>> + * We abuse notification_waitq on group shutdown for waiting for
>> + * all marks pinned when waiting for userspace.
>> + */
>> + if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
>> + wake_up(&group->notification_waitq);
>> }
>> - if (iter_info->vfsmount_mark) {
>> - if (!fsnotify_get_mark_safe(iter_info->vfsmount_mark))
>> - goto out_inode;
>> +}
>> +
>> +bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
>> +{
>> + /* This can fail if mark is being removed */
>> + if (!fsnotify_get_mark_safe(iter_info->inode_mark))
>> + return false;
>> + if (!fsnotify_get_mark_safe(iter_info->vfsmount_mark)) {
>> + fsnotify_put_mark_wait(iter_info->inode_mark);
>> + return false;
>> }
>>
>> /*
>> @@ -292,34 +306,13 @@ bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
>> srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);
>>
>> return true;
>> -out_inode:
>> - if (iter_info->inode_mark)
>> - fsnotify_put_mark(iter_info->inode_mark);
>> -out_wait:
>> - if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
>> - wake_up(&group->notification_waitq);
>> - return false;
>> }
>>
>> void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
>> {
>> - struct fsnotify_group *group = NULL;
>> -
>> iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
>> - if (iter_info->inode_mark) {
>> - group = iter_info->inode_mark->group;
>> - fsnotify_put_mark(iter_info->inode_mark);
>> - }
>> - if (iter_info->vfsmount_mark) {
>> - group = iter_info->vfsmount_mark->group;
>> - fsnotify_put_mark(iter_info->vfsmount_mark);
>> - }
>> - /*
>> - * We abuse notification_waitq on group shutdown for waiting for all
>> - * marks pinned when waiting for userspace.
>> - */
>> - if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
>> - wake_up(&group->notification_waitq);
>> + fsnotify_put_mark_wait(iter_info->inode_mark);
>> + fsnotify_put_mark_wait(iter_info->vfsmount_mark);
>> }
>>
>> /*
>> --
>> 2.5.5
>>
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