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Date:   Fri, 15 Oct 2021 11:46:35 +0200
From:   Jan Kara <jack@suse.cz>
To:     Gabriel Krisman Bertazi <krisman@collabora.com>
Cc:     jack@suse.com, amir73il@gmail.com, djwong@kernel.org,
        tytso@mit.edu, dhowells@redhat.com, khazhy@google.com,
        linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
        linux-api@vger.kernel.org, repnop@google.com, kernel@collabora.com
Subject: Re: [PATCH v7 18/28] fanotify: Pre-allocate pool of error events
Message-ID: <20211015094635.GI23102@quack2.suse.cz>
References: <20211014213646.1139469-1-krisman@collabora.com>
 <20211014213646.1139469-19-krisman@collabora.com>
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On Thu 14-10-21 18:36:36, Gabriel Krisman Bertazi wrote:
> Error reporting needs to be done in an atomic context.  This patch

So this is a requirement I was advocating to remove because although atomic
context is nice for filesystems, it is rather difficult for fanotify.
Instead I was advocating that we relax this and require filesystems to
report errors from a context where using GFP_NOFS allocations is fine. At
least for ext4 and xfs and other filesystems I know it isn't really that
much harder... If this proves to be a problem in some specific case, there
are also other options (like doing notification from a workqueue, events are
async anyway) for the filesystems to take.

> introduces a group-wide mempool of error events, shared by all
> marks in this group.

... "shared by all FS_ERROR marks", right?
 
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>

The code otherwise looks OK to me.

								Honza

> ---
>  fs/notify/fanotify/fanotify.c      |  3 +++
>  fs/notify/fanotify/fanotify.h      | 11 +++++++++++
>  fs/notify/fanotify/fanotify_user.c | 26 +++++++++++++++++++++++++-
>  include/linux/fsnotify_backend.h   |  2 ++
>  4 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index 8f152445d75c..01d68dfc74aa 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -819,6 +819,9 @@ static void fanotify_free_group_priv(struct fsnotify_group *group)
>  	if (group->fanotify_data.ucounts)
>  		dec_ucount(group->fanotify_data.ucounts,
>  			   UCOUNT_FANOTIFY_GROUPS);
> +
> +	if (mempool_initialized(&group->fanotify_data.error_events_pool))
> +		mempool_exit(&group->fanotify_data.error_events_pool);
>  }
>  
>  static void fanotify_free_path_event(struct fanotify_event *event)
> diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
> index c42cf8fd7d79..a577e87fac2b 100644
> --- a/fs/notify/fanotify/fanotify.h
> +++ b/fs/notify/fanotify/fanotify.h
> @@ -141,6 +141,7 @@ 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
>  };
>  
> @@ -196,6 +197,16 @@ FANOTIFY_NE(struct fanotify_event *event)
>  	return container_of(event, struct fanotify_name_event, fae);
>  }
>  
> +struct fanotify_error_event {
> +	struct fanotify_event fae;
> +};
> +
> +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 66ee3c2805c7..f1cf863d6f9f 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -30,6 +30,7 @@
>  #define FANOTIFY_DEFAULT_MAX_EVENTS	16384
>  #define FANOTIFY_OLD_DEFAULT_MAX_MARKS	8192
>  #define FANOTIFY_DEFAULT_MAX_GROUPS	128
> +#define FANOTIFY_DEFAULT_FEE_POOL	32
>  
>  /*
>   * Legacy fanotify marks limits (8192) is per group and we introduced a tunable
> @@ -1054,6 +1055,15 @@ static struct fsnotify_mark *fanotify_add_new_mark(struct fsnotify_group *group,
>  	return ERR_PTR(ret);
>  }
>  
> +static int fanotify_group_init_error_pool(struct fsnotify_group *group)
> +{
> +	if (mempool_initialized(&group->fanotify_data.error_events_pool))
> +		return 0;
> +
> +	return mempool_init_kmalloc_pool(&group->fanotify_data.error_events_pool,
> +					 FANOTIFY_DEFAULT_FEE_POOL,
> +					 sizeof(struct fanotify_error_event));
> +}
>  
>  static int fanotify_add_mark(struct fsnotify_group *group,
>  			     fsnotify_connp_t *connp, unsigned int type,
> @@ -1062,6 +1072,7 @@ 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);
> @@ -1072,13 +1083,26 @@ static int fanotify_add_mark(struct fsnotify_group *group,
>  			return PTR_ERR(fsn_mark);
>  		}
>  	}
> +
> +	/*
> +	 * Error events are pre-allocated per group, only if strictly
> +	 * needed (i.e. FAN_FS_ERROR was requested).
> +	 */
> +	if (!(flags & FAN_MARK_IGNORED_MASK) && (mask & FAN_FS_ERROR)) {
> +		ret = fanotify_group_init_error_pool(group);
> +		if (ret)
> +			goto out;
> +	}
> +
>  	added = fanotify_mark_add_to_mask(fsn_mark, mask, flags);
>  	if (added & ~fsnotify_conn_mask(fsn_mark->connector))
>  		fsnotify_recalc_mask(fsn_mark->connector);
> +
> +out:
>  	mutex_unlock(&group->mark_mutex);
>  
>  	fsnotify_put_mark(fsn_mark);
> -	return 0;
> +	return ret;
>  }
>  
>  static int fanotify_add_vfsmount_mark(struct fsnotify_group *group,
> diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> index a378a314e309..9941c06b8c8a 100644
> --- a/include/linux/fsnotify_backend.h
> +++ b/include/linux/fsnotify_backend.h
> @@ -19,6 +19,7 @@
>  #include <linux/atomic.h>
>  #include <linux/user_namespace.h>
>  #include <linux/refcount.h>
> +#include <linux/mempool.h>
>  
>  /*
>   * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily
> @@ -245,6 +246,7 @@ struct fsnotify_group {
>  			int flags;           /* flags from fanotify_init() */
>  			int f_flags; /* event_f_flags from fanotify_init() */
>  			struct ucounts *ucounts;
> +			mempool_t error_events_pool;
>  		} fanotify_data;
>  #endif /* CONFIG_FANOTIFY */
>  	};
> -- 
> 2.33.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR