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

Amir Goldstein [off-list ref] writes:

On Fri, Oct 15, 2021 at 12:39 AM Gabriel Krisman Bertazi
[off-list ref] wrote:

quoted

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 <redacted>
---
 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