Re: [PATCH v4 3/5] dnotify: move fsnotify_recalc_mask() outside spinlock

Amir Goldstein
2022-11-12T09:07:08Z

On Sat, Nov 12, 2022 at 12:06 AM Stephen Brennan
<stephen.s.brennan@oracle.com> wrote:
>
> In order to allow sleeping during fsnotify_recalc_mask(), we need to
> ensure no callers are holding a spinlock.
>
> Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

small suggestion below.

> ---
> fs/notify/dnotify/dnotify.c | 28 +++++++++++++++++++---------
> 1 file changed, 19 insertions(+), 9 deletions(-)
>
> diff --git a/fs/notify/dnotify/dnotify.c b/fs/notify/dnotify/dnotify.c
> index 190aa717fa32..a9f05b3cf5ea 100644
> --- a/fs/notify/dnotify/dnotify.c
> +++ b/fs/notify/dnotify/dnotify.c
> @@ -58,10 +58,10 @@ struct dnotify_mark {
> * dnotify cares about for that inode may change. This function runs the
> * list of everything receiving dnotify events about this directory and calculates
> * the set of all those events. After it updates what dnotify is interested in
> - * it calls the fsnotify function so it can update the set of all events relevant
> - * to this inode.
> + * it returns true if fsnotify_recalc_mask() should be called to update the set
> + * of all events related to this inode.
> */
> -static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
> +static bool dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
> {
> __u32 new_mask = 0;
> struct dnotify_struct *dn;
> @@ -74,10 +74,9 @@ static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
> for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
> new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
> if (fsn_mark->mask == new_mask)
> - return;
> + return false;
> fsn_mark->mask = new_mask;
> -
> - fsnotify_recalc_mask(fsn_mark->connector);
> + return true;
> }
>
> /*
> @@ -97,6 +96,7 @@ static int dnotify_handle_event(struct fsnotify_mark *inode_mark, u32 mask,
> struct dnotify_struct **prev;
> struct fown_struct *fown;
> __u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
> + bool recalc = false;
>
> /* not a dir, dnotify doesn't care */
> if (!dir && !(mask & FS_ISDIR))
> @@ -118,12 +118,15 @@ static int dnotify_handle_event(struct fsnotify_mark *inode_mark, u32 mask,
> else {
> *prev = dn->dn_next;
> kmem_cache_free(dnotify_struct_cache, dn);
> - dnotify_recalc_inode_mask(inode_mark);
> + recalc = dnotify_recalc_inode_mask(inode_mark);
> }
> }
>
> spin_unlock(&inode_mark->lock);
>
> + if (recalc)
> + fsnotify_recalc_mask(inode_mark->connector);
> +
> return 0;
> }
>
> @@ -158,6 +161,7 @@ void dnotify_flush(struct file *filp, fl_owner_t id)
> struct dnotify_struct **prev;
> struct inode *inode;
> bool free = false;
> + bool recalc = false;
>
> inode = file_inode(filp);
> if (!S_ISDIR(inode->i_mode))
> @@ -176,7 +180,7 @@ void dnotify_flush(struct file *filp, fl_owner_t id)
> if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
> *prev = dn->dn_next;
> kmem_cache_free(dnotify_struct_cache, dn);
> - dnotify_recalc_inode_mask(fsn_mark);
> + recalc = dnotify_recalc_inode_mask(fsn_mark);
> break;
> }
> prev = &dn->dn_next;
> @@ -184,6 +188,9 @@ void dnotify_flush(struct file *filp, fl_owner_t id)
>
> spin_unlock(&fsn_mark->lock);
>
> + if (recalc)
> + fsnotify_recalc_mask(fsn_mark->connector);
> +
> /* nothing else could have found us thanks to the dnotify_groups
> mark_mutex */
> if (dn_mark->dn == NULL) {
> @@ -268,6 +275,7 @@ int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
> struct file *f;
> int destroy = 0, error = 0;
> __u32 mask;
> + bool recalc = false;
>
> /* we use these to tell if we need to kfree */
> new_fsn_mark = NULL;
> @@ -377,9 +385,11 @@ int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
> else if (error == -EEXIST)
> error = 0;
>
> - dnotify_recalc_inode_mask(fsn_mark);
> + recalc = dnotify_recalc_inode_mask(fsn_mark);
> out:
> spin_unlock(&fsn_mark->lock);
> + if (recalc)
> + fsnotify_recalc_mask(fsn_mark->connector);
>
> if (destroy)
> fsnotify_detach_mark(fsn_mark);

I'd do else if (recalc)

just to emphasise that destroy and recalc are mutually exclusive.

Thanks,
Amir.