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Date: Fri, 15 Oct 2021 11:46:35 +0200
From: Jan Kara <jack@...e.cz>
To: Gabriel Krisman Bertazi <krisman@...labora.com>
Cc: jack@...e.com, amir73il@...il.com, djwong@...nel.org,
tytso@....edu, dhowells@...hat.com, khazhy@...gle.com,
linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
linux-api@...r.kernel.org, repnop@...gle.com, kernel@...labora.com
Subject: Re: [PATCH v7 18/28] fanotify: Pre-allocate pool of error events
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@...labora.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@...e.com>
SUSE Labs, CR
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