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Date:   Fri, 13 Aug 2021 11:40:30 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Jan Kara <jack@...e.com>, Linux API <linux-api@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        Theodore Tso <tytso@....edu>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Matthew Bobrowski <repnop@...gle.com>, kernel@...labora.com
Subject: Re: [PATCH v6 15/21] fanotify: Preallocate per superblock mark error event

On Fri, Aug 13, 2021 at 12:41 AM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Error reporting needs to be done in an atomic context.  This patch
> introduces a single error slot for superblock marks that report the
> FAN_FS_ERROR event, to be used during event submission.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>
> ---
> Changes v5:
>   - Restore mark references. (jan)
>   - Tie fee slot to the mark lifetime.(jan)
>   - Don't reallocate event(jan)
> ---
>  fs/notify/fanotify/fanotify.c      | 12 ++++++++++++
>  fs/notify/fanotify/fanotify.h      | 13 +++++++++++++
>  fs/notify/fanotify/fanotify_user.c | 31 ++++++++++++++++++++++++++++--
>  3 files changed, 54 insertions(+), 2 deletions(-)
>
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index ebb6c557cea1..3bf6fd85c634 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -855,6 +855,14 @@ static void fanotify_free_name_event(struct fanotify_event *event)
>         kfree(FANOTIFY_NE(event));
>  }
>
> +static void fanotify_free_error_event(struct fanotify_event *event)
> +{
> +       /*
> +        * The actual event is tied to a mark, and is released on mark
> +        * removal
> +        */
> +}
> +
>  static void fanotify_free_event(struct fsnotify_event *fsn_event)
>  {
>         struct fanotify_event *event;
> @@ -877,6 +885,9 @@ static void fanotify_free_event(struct fsnotify_event *fsn_event)
>         case FANOTIFY_EVENT_TYPE_OVERFLOW:
>                 kfree(event);
>                 break;
> +       case FANOTIFY_EVENT_TYPE_FS_ERROR:
> +               fanotify_free_error_event(event);
> +               break;
>         default:
>                 WARN_ON_ONCE(1);
>         }
> @@ -894,6 +905,7 @@ static void fanotify_free_mark(struct fsnotify_mark *mark)
>         if (mark->flags & FANOTIFY_MARK_FLAG_SB_MARK) {
>                 struct fanotify_sb_mark *fa_mark = FANOTIFY_SB_MARK(mark);
>
> +               kfree(fa_mark->fee_slot);
>                 kmem_cache_free(fanotify_sb_mark_cache, fa_mark);
>         } else {
>                 kmem_cache_free(fanotify_mark_cache, mark);
> diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
> index b3ab620822c2..3f03333df32f 100644
> --- a/fs/notify/fanotify/fanotify.h
> +++ b/fs/notify/fanotify/fanotify.h
> @@ -139,6 +139,7 @@ enum fanotify_mark_bits {
>
>  struct fanotify_sb_mark {
>         struct fsnotify_mark fsn_mark;
> +       struct fanotify_error_event *fee_slot;
>  };
>
>  static inline
> @@ -161,6 +162,7 @@ enum fanotify_event_type {
>         FANOTIFY_EVENT_TYPE_PATH,
>         FANOTIFY_EVENT_TYPE_PATH_PERM,
>         FANOTIFY_EVENT_TYPE_OVERFLOW, /* struct fanotify_event */
> +       FANOTIFY_EVENT_TYPE_FS_ERROR, /* struct fanotify_error_event */
>         __FANOTIFY_EVENT_TYPE_NUM
>  };
>
> @@ -216,6 +218,17 @@ FANOTIFY_NE(struct fanotify_event *event)
>         return container_of(event, struct fanotify_name_event, fae);
>  }
>
> +struct fanotify_error_event {
> +       struct fanotify_event fae;
> +       struct fanotify_sb_mark *sb_mark; /* Back reference to the mark. */
> +};
> +
> +static inline struct fanotify_error_event *
> +FANOTIFY_EE(struct fanotify_event *event)
> +{
> +       return container_of(event, struct fanotify_error_event, fae);
> +}
> +
>  static inline __kernel_fsid_t *fanotify_event_fsid(struct fanotify_event *event)
>  {
>         if (event->type == FANOTIFY_EVENT_TYPE_FID)
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index 54107f1533d5..b77030386d7f 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -947,8 +947,10 @@ static struct fsnotify_mark *fanotify_alloc_mark(struct fsnotify_group *group,
>
>         fsnotify_init_mark(mark, group);
>
> -       if (type == FSNOTIFY_OBJ_TYPE_SB)
> +       if (type == FSNOTIFY_OBJ_TYPE_SB) {
>                 mark->flags |= FANOTIFY_MARK_FLAG_SB_MARK;
> +               sb_mark->fee_slot = NULL;
> +       }
>
>         return mark;
>  }
> @@ -999,6 +1001,7 @@ static int fanotify_add_mark(struct fsnotify_group *group,
>  {
>         struct fsnotify_mark *fsn_mark;
>         __u32 added;
> +       int ret = 0;
>
>         mutex_lock(&group->mark_mutex);
>         fsn_mark = fsnotify_find_mark(connp, group);
> @@ -1009,13 +1012,37 @@ static int fanotify_add_mark(struct fsnotify_group *group,
>                         return PTR_ERR(fsn_mark);
>                 }
>         }
> +
> +       /*
> +        * Error events are allocated per super-block mark only if
> +        * strictly needed (i.e. FAN_FS_ERROR was requested).
> +        */
> +       if (type == FSNOTIFY_OBJ_TYPE_SB && !(flags & FAN_MARK_IGNORED_MASK) &&
> +           (mask & FAN_FS_ERROR)) {
> +               struct fanotify_sb_mark *sb_mark = FANOTIFY_SB_MARK(fsn_mark);
> +
> +               if (!sb_mark->fee_slot) {
> +                       struct fanotify_error_event *fee =
> +                               kzalloc(sizeof(*fee), GFP_KERNEL_ACCOUNT);
> +                       if (!fee) {
> +                               ret = -ENOMEM;
> +                               goto out;
> +                       }
> +                       fanotify_init_event(&fee->fae, 0, FS_ERROR);
> +                       fee->sb_mark = sb_mark;

I think Jan wanted to avoid zalloc()?
Please use kmalloc() and init the rest of the fee-> members.
We do not need to fill the entire fh buf with zeroes.

Thanks,
Amir.

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