ping?
Hi Greg,
I have no idea of this patch since Matthew makes no response after
modification... And this series is still not backported to 4.19 till now...
What should I do next? Can this series be accepted for linux-4.19? :(
Thanks,
Gao Xiang
On 2019/3/14 12:42, Gao Xiang wrote:
> commit 51232df5e4b268936beccde5248f312a316800be upstream.
>
> When the managed cache is enabled, the last reference count
> of a workgroup must be used for its workstation.
>
> Otherwise, it could lead to incorrect (un)freezes in
> the reclaim path, and it would be harmful.
>
> A typical race as follows:
>
> Thread 1 (In the reclaim path) Thread 2
> workgroup_freeze(grp, 1) refcnt = 1
> ...
> workgroup_unfreeze(grp, 1) refcnt = 1
> workgroup_get(grp) refcnt = 2 (x)
> workgroup_put(grp) refcnt = 1 (x)
> ...unexpected behaviors
>
> * grp is detached but still used, which violates cache-managed
> freeze constraint.
>
> Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
> ---
> drivers/staging/erofs/internal.h | 1 +
> drivers/staging/erofs/utils.c | 134 +++++++++++++++++++++++++++------------
> 2 files changed, 96 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
> index c70f0c5237ea..58d8cbc3f921 100644
> --- a/drivers/staging/erofs/internal.h
> +++ b/drivers/staging/erofs/internal.h
> @@ -260,6 +260,7 @@ static inline bool erofs_workgroup_get(struct erofs_workgroup *grp, int *ocnt)
> }
>
> #define __erofs_workgroup_get(grp) atomic_inc(&(grp)->refcount)
> +#define __erofs_workgroup_put(grp) atomic_dec(&(grp)->refcount)
>
> extern int erofs_workgroup_put(struct erofs_workgroup *grp);
>
> diff --git a/drivers/staging/erofs/utils.c b/drivers/staging/erofs/utils.c
> index c466e8c8ea90..71c7fe0b61c3 100644
> --- a/drivers/staging/erofs/utils.c
> +++ b/drivers/staging/erofs/utils.c
> @@ -83,12 +83,21 @@ int erofs_register_workgroup(struct super_block *sb,
>
> grp = xa_tag_pointer(grp, tag);
>
> - err = radix_tree_insert(&sbi->workstn_tree,
> - grp->index, grp);
> + /*
> + * Bump up reference count before making this workgroup
> + * visible to other users in order to avoid potential UAF
> + * without serialized by erofs_workstn_lock.
> + */
> + __erofs_workgroup_get(grp);
>
> - if (!err) {
> - __erofs_workgroup_get(grp);
> - }
> + err = radix_tree_insert(&sbi->workstn_tree,
> + grp->index, grp);
> + if (unlikely(err))
> + /*
> + * it's safe to decrease since the workgroup isn't visible
> + * and refcount >= 2 (cannot be freezed).
> + */
> + __erofs_workgroup_put(grp);
>
> erofs_workstn_unlock(sbi);
> radix_tree_preload_end();
> @@ -97,19 +106,94 @@ int erofs_register_workgroup(struct super_block *sb,
>
> extern void erofs_workgroup_free_rcu(struct erofs_workgroup *grp);
>
> +static void __erofs_workgroup_free(struct erofs_workgroup *grp)
> +{
> + atomic_long_dec(&erofs_global_shrink_cnt);
> + erofs_workgroup_free_rcu(grp);
> +}
> +
> int erofs_workgroup_put(struct erofs_workgroup *grp)
> {
> int count = atomic_dec_return(&grp->refcount);
>
> if (count == 1)
> atomic_long_inc(&erofs_global_shrink_cnt);
> - else if (!count) {
> - atomic_long_dec(&erofs_global_shrink_cnt);
> - erofs_workgroup_free_rcu(grp);
> - }
> + else if (!count)
> + __erofs_workgroup_free(grp);
> return count;
> }
>
> +#ifdef EROFS_FS_HAS_MANAGED_CACHE
> +/* for cache-managed case, customized reclaim paths exist */
> +static void erofs_workgroup_unfreeze_final(struct erofs_workgroup *grp)
> +{
> + erofs_workgroup_unfreeze(grp, 0);
> + __erofs_workgroup_free(grp);
> +}
> +
> +bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
> + struct erofs_workgroup *grp,
> + bool cleanup)
> +{
> + /*
> + * for managed cache enabled, the refcount of workgroups
> + * themselves could be < 0 (freezed). So there is no guarantee
> + * that all refcount > 0 if managed cache is enabled.
> + */
> + if (!erofs_workgroup_try_to_freeze(grp, 1))
> + return false;
> +
> + /*
> + * note that all cached pages should be unlinked
> + * before delete it from the radix tree.
> + * Otherwise some cached pages of an orphan old workgroup
> + * could be still linked after the new one is available.
> + */
> + if (erofs_try_to_free_all_cached_pages(sbi, grp)) {
> + erofs_workgroup_unfreeze(grp, 1);
> + return false;
> + }
> +
> + /*
> + * it is impossible to fail after the workgroup is freezed,
> + * however in order to avoid some race conditions, add a
> + * DBG_BUGON to observe this in advance.
> + */
> + DBG_BUGON(xa_untag_pointer(radix_tree_delete(&sbi->workstn_tree,
> + grp->index)) != grp);
> +
> + /*
> + * if managed cache is enable, the last refcount
> + * should indicate the related workstation.
> + */
> + erofs_workgroup_unfreeze_final(grp);
> + return true;
> +}
> +
> +#else
> +/* for nocache case, no customized reclaim path at all */
> +bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
> + struct erofs_workgroup *grp,
> + bool cleanup)
> +{
> + int cnt = atomic_read(&grp->refcount);
> +
> + DBG_BUGON(cnt <= 0);
> + DBG_BUGON(cleanup && cnt != 1);
> +
> + if (cnt > 1)
> + return false;
> +
> + DBG_BUGON(xa_untag_pointer(radix_tree_delete(&sbi->workstn_tree,
> + grp->index)) != grp);
> +
> + /* (rarely) could be grabbed again when freeing */
> + erofs_workgroup_put(grp);
> + return true;
> +}
> +
> +#endif
> +
> unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
> unsigned long nr_shrink,
> bool cleanup)
> @@ -126,42 +210,14 @@ unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
> batch, first_index, PAGEVEC_SIZE);
>
> for (i = 0; i < found; ++i) {
> - int cnt;
> struct erofs_workgroup *grp = xa_untag_pointer(batch[i]);
>
> first_index = grp->index + 1;
>
> - cnt = atomic_read(&grp->refcount);
> - BUG_ON(cnt <= 0);
> -
> - if (cleanup)
> - BUG_ON(cnt != 1);
> -
> -#ifndef EROFS_FS_HAS_MANAGED_CACHE
> - else if (cnt > 1)
> -#else
> - if (!erofs_workgroup_try_to_freeze(grp, 1))
> -#endif
> + /* try to shrink each valid workgroup */
> + if (!erofs_try_to_release_workgroup(sbi, grp, cleanup))
> continue;
>
> - if (xa_untag_pointer(radix_tree_delete(&sbi->workstn_tree,
> - grp->index)) != grp) {
> -#ifdef EROFS_FS_HAS_MANAGED_CACHE
> -skip:
> - erofs_workgroup_unfreeze(grp, 1);
> -#endif
> - continue;
> - }
> -
> -#ifdef EROFS_FS_HAS_MANAGED_CACHE
> - if (erofs_try_to_free_all_cached_pages(sbi, grp))
> - goto skip;
> -
> - erofs_workgroup_unfreeze(grp, 1);
> -#endif
> - /* (rarely) grabbed again when freeing */
> - erofs_workgroup_put(grp);
> -
> ++freed;
> if (unlikely(!--nr_shrink))
> break;
>
