Re: [PATCH v7 19/28] fanotify: Limit number of marks with FAN_FS_ERROR per group

[Gabriel Krisman Bertazi <krisman@collabora.com>]

Amir Goldstein <amir73il@gmail.com> writes:

> On Fri, Oct 15, 2021 at 12:39 AM Gabriel Krisman Bertazi
> <krisman@collabora.com> wrote:
>>
>> Since FAN_FS_ERROR memory must be pre-allocated, limit a single group
>> from watching too many file systems at once.  The current scheme
>> guarantees 1 slot per filesystem, so limit the number of marks with
>> FAN_FS_ERROR per group.
>>
>> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
>> ---
>>  fs/notify/fanotify/fanotify_user.c | 10 ++++++++++
>>  include/linux/fsnotify_backend.h   |  1 +
>>  2 files changed, 11 insertions(+)
>>
>> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
>> index f1cf863d6f9f..5324890500fc 100644
>> --- a/fs/notify/fanotify/fanotify_user.c
>> +++ b/fs/notify/fanotify/fanotify_user.c
>> @@ -959,6 +959,10 @@ static int fanotify_remove_mark(struct fsnotify_group *group,
>>
>>         removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags,
>>                                                  umask, &destroy_mark);
>> +
>> +       if (removed & FAN_FS_ERROR)
>> +               group->fanotify_data.error_event_marks--;
>> +
>>         if (removed & fsnotify_conn_mask(fsn_mark->connector))
>>                 fsnotify_recalc_mask(fsn_mark->connector);
>>         if (destroy_mark)
>> @@ -1057,6 +1061,9 @@ static struct fsnotify_mark *fanotify_add_new_mark(struct fsnotify_group *group,
>>
>>  static int fanotify_group_init_error_pool(struct fsnotify_group *group)
>>  {
>> +       if (group->fanotify_data.error_event_marks >= FANOTIFY_DEFAULT_FEE_POOL)
>> +               return -ENOMEM;
>
> Why not try to mempool_resize()?

Jan suggested we might not need to bother with it, but I can do that for
the next version.

> Also, I did not read the rest of the patches yet, but don't we need two
> slots per mark? one for alloc-pre-enqueue and one for free-post-dequeue?

I don't understand what you mean by two slots for alloc-pre-enqueue and
free-post-dequeue.  I suspect it is no longer necessary now that
FAN_FS_ERROR is handled like any other event on enqueue/dequeue, but can
you confirm or clarify?

Thanks,

-- 
Gabriel Krisman Bertazi