| Message ID | 20150722211538.GA20014@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed 22-07-15 23:15:38, Oleg Nesterov wrote: > Of course, this patch is ugly as hell. It will be (partially) > reverted later. We add it to ensure that other WIP changes in > percpu_rw_semaphore won't break fs/super.c. > > We do not even need this change right now, percpu_free_rwsem() > is fine in atomic context. But we are going to change this, it > will be might_sleep() after we merge the rcu_sync() patches. > > And even after that we do not really need destroy_super_work(), > we will kill it in any case. Instead, destroy_super_rcu() should > just check that rss->cb_state == CB_IDLE and do call_rcu() again > in the (very unlikely) case this is not true. > > So this is just the temporary kludge which helps us to avoid the > conflicts with the changes which will be (hopefully) routed via > rcu tree. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com> OK, looks acceptable to me. You can add: Reviewed-by: Jan Kara <jack@suse.com> Honza > --- > fs/super.c | 23 +++++++++++++++++++---- > include/linux/fs.h | 3 ++- > 2 files changed, 21 insertions(+), 5 deletions(-) > > diff --git a/fs/super.c b/fs/super.c > index b4db3ee..886fddf 100644 > --- a/fs/super.c > +++ b/fs/super.c > @@ -135,6 +135,24 @@ static unsigned long super_cache_count(struct shrinker *shrink, > return total_objects; > } > > +static void destroy_super_work(struct work_struct *work) > +{ > + struct super_block *s = container_of(work, struct super_block, > + destroy_work); > + int i; > + > + for (i = 0; i < SB_FREEZE_LEVELS; i++) > + percpu_counter_destroy(&s->s_writers.counter[i]); > + kfree(s); > +} > + > +static void destroy_super_rcu(struct rcu_head *head) > +{ > + struct super_block *s = container_of(head, struct super_block, rcu); > + INIT_WORK(&s->destroy_work, destroy_super_work); > + schedule_work(&s->destroy_work); > +} > + > /** > * destroy_super - frees a superblock > * @s: superblock to free > @@ -143,16 +161,13 @@ static unsigned long super_cache_count(struct shrinker *shrink, > */ > static void destroy_super(struct super_block *s) > { > - int i; > list_lru_destroy(&s->s_dentry_lru); > list_lru_destroy(&s->s_inode_lru); > - for (i = 0; i < SB_FREEZE_LEVELS; i++) > - percpu_counter_destroy(&s->s_writers.counter[i]); > security_sb_free(s); > WARN_ON(!list_empty(&s->s_mounts)); > kfree(s->s_subtype); > kfree(s->s_options); > - kfree_rcu(s, rcu); > + call_rcu(&s->rcu, destroy_super_rcu); > } > > /** > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 78ac768..6addccc 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -30,6 +30,7 @@ > #include <linux/lockdep.h> > #include <linux/percpu-rwsem.h> > #include <linux/blk_types.h> > +#include <linux/workqueue.h> > > #include <asm/byteorder.h> > #include <uapi/linux/fs.h> > @@ -1346,7 +1347,7 @@ struct super_block { > struct list_lru s_dentry_lru ____cacheline_aligned_in_smp; > struct list_lru s_inode_lru ____cacheline_aligned_in_smp; > struct rcu_head rcu; > - > + struct work_struct destroy_work; > /* > * Indicates how deep in a filesystem stack this SB is > */ > -- > 1.5.5.1 >
diff --git a/fs/super.c b/fs/super.c index b4db3ee..886fddf 100644 --- a/fs/super.c +++ b/fs/super.c @@ -135,6 +135,24 @@ static unsigned long super_cache_count(struct shrinker *shrink, return total_objects; } +static void destroy_super_work(struct work_struct *work) +{ + struct super_block *s = container_of(work, struct super_block, + destroy_work); + int i; + + for (i = 0; i < SB_FREEZE_LEVELS; i++) + percpu_counter_destroy(&s->s_writers.counter[i]); + kfree(s); +} + +static void destroy_super_rcu(struct rcu_head *head) +{ + struct super_block *s = container_of(head, struct super_block, rcu); + INIT_WORK(&s->destroy_work, destroy_super_work); + schedule_work(&s->destroy_work); +} + /** * destroy_super - frees a superblock * @s: superblock to free @@ -143,16 +161,13 @@ static unsigned long super_cache_count(struct shrinker *shrink, */ static void destroy_super(struct super_block *s) { - int i; list_lru_destroy(&s->s_dentry_lru); list_lru_destroy(&s->s_inode_lru); - for (i = 0; i < SB_FREEZE_LEVELS; i++) - percpu_counter_destroy(&s->s_writers.counter[i]); security_sb_free(s); WARN_ON(!list_empty(&s->s_mounts)); kfree(s->s_subtype); kfree(s->s_options); - kfree_rcu(s, rcu); + call_rcu(&s->rcu, destroy_super_rcu); } /** diff --git a/include/linux/fs.h b/include/linux/fs.h index 78ac768..6addccc 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -30,6 +30,7 @@ #include <linux/lockdep.h> #include <linux/percpu-rwsem.h> #include <linux/blk_types.h> +#include <linux/workqueue.h> #include <asm/byteorder.h> #include <uapi/linux/fs.h> @@ -1346,7 +1347,7 @@ struct super_block { struct list_lru s_dentry_lru ____cacheline_aligned_in_smp; struct list_lru s_inode_lru ____cacheline_aligned_in_smp; struct rcu_head rcu; - + struct work_struct destroy_work; /* * Indicates how deep in a filesystem stack this SB is */
Of course, this patch is ugly as hell. It will be (partially) reverted later. We add it to ensure that other WIP changes in percpu_rw_semaphore won't break fs/super.c. We do not even need this change right now, percpu_free_rwsem() is fine in atomic context. But we are going to change this, it will be might_sleep() after we merge the rcu_sync() patches. And even after that we do not really need destroy_super_work(), we will kill it in any case. Instead, destroy_super_rcu() should just check that rss->cb_state == CB_IDLE and do call_rcu() again in the (very unlikely) case this is not true. So this is just the temporary kludge which helps us to avoid the conflicts with the changes which will be (hopefully) routed via rcu tree. Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- fs/super.c | 23 +++++++++++++++++++---- include/linux/fs.h | 3 ++- 2 files changed, 21 insertions(+), 5 deletions(-)