linux-kernel - Re: [PATCH 2/4] fsnotify: skip unattached marks

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Date:   Fri, 20 Oct 2017 15:05:55 +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 2/4] fsnotify: skip unattached marks

On Thu, Oct 19, 2017 at 4:58 PM, Miklos Szeredi <mszeredi@...hat.com> wrote:
> After having gone through a ref-unref for the mark, dereferencing the group
> (e.g. in fsnotify_compare_groups()) is wrong since the group may be
> completely gone by that time.  So before continuing to traverse the mark
> list, check if the mark is still attached.
>
> This is done in the generic case, not just when we go through
> fsnotify_prepare_user_wait()/fsnotify_finish_user_wait(), otherwise it
> would introduce unnecessary complexity.  And it shouldn't hurt to skip
> unattached marks anyway ("flags" is very likely in same cacheline as
> neighbouring "ignored_mask", which is pulled in anyway).
>

Looks good.

> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> Fixes: 9385a84d7e1f ("fsnotify: Pass fsnotify_iter_info into handle_event handler")

I don't know that *this* is the commit that this patch "Fixes"
but for the purpose of determining if fix patch should be applied or
not I guess it will do

> Cc: <stable@...r.kernel.org> # v4.12
> ---
>  fs/notify/fsnotify.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
> index 48ec61f4c4d5..0ab6a7179e4d 100644
> --- a/fs/notify/fsnotify.c
> +++ b/fs/notify/fsnotify.c
> @@ -328,12 +328,16 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
>                         inode_mark = hlist_entry(srcu_dereference(inode_node, &fsnotify_mark_srcu),
>                                                  struct fsnotify_mark, obj_list);
>                         inode_group = inode_mark->group;
> +                       if (!(inode_mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED))
> +                               goto skip_inode;
>                 }
>
>                 if (vfsmount_node) {
>                         vfsmount_mark = hlist_entry(srcu_dereference(vfsmount_node, &fsnotify_mark_srcu),
>                                                     struct fsnotify_mark, obj_list);
>                         vfsmount_group = vfsmount_mark->group;
> +                       if (!(vfsmount_mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED))
> +                               goto skip_vfsmount;
>                 }
>
>                 iter_info.inode_mark = inode_mark;
> @@ -357,10 +361,11 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
>
>                 if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
>                         goto out;
> -
> +skip_inode:
>                 if (inode_group)
>                         inode_node = srcu_dereference(inode_node->next,
>                                                       &fsnotify_mark_srcu);
> +skip_vfsmount:
>                 if (vfsmount_group)
>                         vfsmount_node = srcu_dereference(vfsmount_node->next,
>                                                          &fsnotify_mark_srcu);
> --
> 2.5.5
>