Re: [PATCH v7 21/28] fanotify: Support merging of error events

From: Gabriel Krisman Bertazi <krisman@collabora.com>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Jan Kara <jack@suse.com>, "Darrick J. Wong" <djwong@kernel.org>,
	Theodore Tso <tytso@mit.edu>, David Howells <dhowells@redhat.com>,
	Khazhismel Kumykov <khazhy@google.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Ext4 <linux-ext4@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Matthew Bobrowski <repnop@google.com>,
	kernel@collabora.com
Subject: Re: [PATCH v7 21/28] fanotify: Support merging of error events
Date: Mon, 18 Oct 2021 10:55:06 -0300	[thread overview]
Message-ID: <87ee8iphdx.fsf@collabora.com> (raw)
In-Reply-To: <CAOQ4uxizDrR=cnPQzSx8C7-b3fUCWujvpKeCrq0kcMK8kw3=mw@mail.gmail.com> (Amir Goldstein's message of "Fri, 15 Oct 2021 20:52:43 +0300")

Amir Goldstein <amir73il@gmail.com> writes:

> On Fri, Oct 15, 2021 at 7:54 PM Gabriel Krisman Bertazi
> <krisman@collabora.com> wrote:
>>
>> Amir Goldstein <amir73il@gmail.com> writes:
>>
>> > On Fri, Oct 15, 2021 at 12:39 AM Gabriel Krisman Bertazi
>> > <krisman@collabora.com> wrote:
>> >>
>> >> Error events (FAN_FS_ERROR) against the same file system can be merged
>> >> by simply iterating the error count.  The hash is taken from the fsid,
>> >> without considering the FH.  This means that only the first error object
>> >> is reported.
>> >>
>> >> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
>> >> ---
>> >>  fs/notify/fanotify/fanotify.c | 39 ++++++++++++++++++++++++++++++++---
>> >>  fs/notify/fanotify/fanotify.h |  4 +++-
>> >>  2 files changed, 39 insertions(+), 4 deletions(-)
>> >>
>> >> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
>> >> index 9b970359570a..7032083df62a 100644
>> >> --- a/fs/notify/fanotify/fanotify.c
>> >> +++ b/fs/notify/fanotify/fanotify.c
>> >> @@ -111,6 +111,16 @@ static bool fanotify_name_event_equal(struct fanotify_name_event *fne1,
>> >>         return fanotify_info_equal(info1, info2);
>> >>  }
>> >>
>> >> +static bool fanotify_error_event_equal(struct fanotify_error_event *fee1,
>> >> +                                      struct fanotify_error_event *fee2)
>> >> +{
>> >> +       /* Error events against the same file system are always merged. */
>> >> +       if (!fanotify_fsid_equal(&fee1->fsid, &fee2->fsid))
>> >> +               return false;
>> >> +
>> >> +       return true;
>> >> +}
>> >> +
>> >>  static bool fanotify_should_merge(struct fanotify_event *old,
>> >>                                   struct fanotify_event *new)
>> >>  {
>> >> @@ -141,6 +151,9 @@ static bool fanotify_should_merge(struct fanotify_event *old,
>> >>         case FANOTIFY_EVENT_TYPE_FID_NAME:
>> >>                 return fanotify_name_event_equal(FANOTIFY_NE(old),
>> >>                                                  FANOTIFY_NE(new));
>> >> +       case FANOTIFY_EVENT_TYPE_FS_ERROR:
>> >> +               return fanotify_error_event_equal(FANOTIFY_EE(old),
>> >> +                                                 FANOTIFY_EE(new));
>> >>         default:
>> >>                 WARN_ON_ONCE(1);
>> >>         }
>> >> @@ -148,6 +161,22 @@ static bool fanotify_should_merge(struct fanotify_event *old,
>> >>         return false;
>> >>  }
>> >>
>> >> +static void fanotify_merge_error_event(struct fanotify_error_event *dest,
>> >> +                                      struct fanotify_error_event *origin)
>> >> +{
>> >> +       dest->err_count++;
>> >> +}
>> >> +
>> >> +static void fanotify_merge_event(struct fanotify_event *dest,
>> >> +                                struct fanotify_event *origin)
>> >> +{
>> >> +       dest->mask |= origin->mask;
>> >> +
>> >> +       if (origin->type == FANOTIFY_EVENT_TYPE_FS_ERROR)
>> >> +               fanotify_merge_error_event(FANOTIFY_EE(dest),
>> >> +                                          FANOTIFY_EE(origin));
>> >> +}
>> >> +
>> >>  /* Limit event merges to limit CPU overhead per event */
>> >>  #define FANOTIFY_MAX_MERGE_EVENTS 128
>> >>
>> >> @@ -175,7 +204,7 @@ static int fanotify_merge(struct fsnotify_group *group,
>> >>                 if (++i > FANOTIFY_MAX_MERGE_EVENTS)
>> >>                         break;
>> >>                 if (fanotify_should_merge(old, new)) {
>> >> -                       old->mask |= new->mask;
>> >> +                       fanotify_merge_event(old, new);
>> >>                         return 1;
>> >>                 }
>> >>         }
>> >> @@ -577,7 +606,8 @@ static struct fanotify_event *fanotify_alloc_name_event(struct inode *id,
>> >>  static struct fanotify_event *fanotify_alloc_error_event(
>> >>                                                 struct fsnotify_group *group,
>> >>                                                 __kernel_fsid_t *fsid,
>> >> -                                               const void *data, int data_type)
>> >> +                                               const void *data, int data_type,
>> >> +                                               unsigned int *hash)
>> >>  {
>> >>         struct fs_error_report *report =
>> >>                         fsnotify_data_error_report(data, data_type);
>> >> @@ -591,6 +621,9 @@ static struct fanotify_event *fanotify_alloc_error_event(
>> >>                 return NULL;
>> >>
>> >>         fee->fae.type = FANOTIFY_EVENT_TYPE_FS_ERROR;
>> >> +       fee->err_count = 1;
>> >> +
>> >> +       *hash ^= fanotify_hash_fsid(fsid);
>> >>
>> >>         return &fee->fae;
>> >>  }
>> >
>> > Forgot to store fee->fsid?
>>
>> Not really. this is part of the FID info record support, which is done
>> in patch 23.
>>
>
> Sure, it does not really matter for bisection when FS_ERROR is not yet
> wired, but it is weird to compare event fsid's when they have not been
> initialized.
>
> Logically, storing the fsid in this patch would be better.

Makes sense.  Will do!

Thanks,

-- 
Gabriel Krisman Bertazi