From: Christoph Hellwig <hch@xxxxxx> Subject: mm: simplify bdi refcounting Move grabbing and releasing the bdi refcount out of the common wb_init/wb_exit helpers into code that is only used for the non-default memcg driven bdi_writeback structures. [hch@xxxxxx: add comment] Link: https://lkml.kernel.org/r/20211027074207.GA12793@xxxxxx [akpm@xxxxxxxxxxxxxxxxxxxx: fix typo] Link: https://lkml.kernel.org/r/20211021124441.668816-6-hch@xxxxxx Signed-off-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Cc: Miquel Raynal <miquel.raynal@xxxxxxxxxxx> Cc: Richard Weinberger <richard@xxxxxx> Cc: Vignesh Raghavendra <vigneshr@xxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/backing-dev-defs.h | 3 +++ mm/backing-dev.c | 13 +++++-------- 2 files changed, 8 insertions(+), 8 deletions(-) --- a/include/linux/backing-dev-defs.h~mm-simplify-bdi-refcounting +++ a/include/linux/backing-dev-defs.h @@ -103,6 +103,9 @@ struct wb_completion { * change as blkcg is disabled and enabled higher up in the hierarchy, a wb * is tested for blkcg after lookup and removed from index on mismatch so * that a new wb for the combination can be created. + * + * Each bdi_writeback that is not embedded into the backing_dev_info must hold + * a reference to the parent backing_dev_info. See cgwb_create() for details. */ struct bdi_writeback { struct backing_dev_info *bdi; /* our parent bdi */ --- a/mm/backing-dev.c~mm-simplify-bdi-refcounting +++ a/mm/backing-dev.c @@ -291,8 +291,6 @@ static int wb_init(struct bdi_writeback memset(wb, 0, sizeof(*wb)); - if (wb != &bdi->wb) - bdi_get(bdi); wb->bdi = bdi; wb->last_old_flush = jiffies; INIT_LIST_HEAD(&wb->b_dirty); @@ -316,7 +314,7 @@ static int wb_init(struct bdi_writeback err = fprop_local_init_percpu(&wb->completions, gfp); if (err) - goto out_put_bdi; + return err; for (i = 0; i < NR_WB_STAT_ITEMS; i++) { err = percpu_counter_init(&wb->stat[i], 0, gfp); @@ -330,9 +328,6 @@ out_destroy_stat: while (i--) percpu_counter_destroy(&wb->stat[i]); fprop_local_destroy_percpu(&wb->completions); -out_put_bdi: - if (wb != &bdi->wb) - bdi_put(bdi); return err; } @@ -373,8 +368,6 @@ static void wb_exit(struct bdi_writeback percpu_counter_destroy(&wb->stat[i]); fprop_local_destroy_percpu(&wb->completions); - if (wb != &wb->bdi->wb) - bdi_put(wb->bdi); } #ifdef CONFIG_CGROUP_WRITEBACK @@ -397,6 +390,7 @@ static void cgwb_release_workfn(struct w struct bdi_writeback *wb = container_of(work, struct bdi_writeback, release_work); struct blkcg *blkcg = css_to_blkcg(wb->blkcg_css); + struct backing_dev_info *bdi = wb->bdi; mutex_lock(&wb->bdi->cgwb_release_mutex); wb_shutdown(wb); @@ -416,6 +410,7 @@ static void cgwb_release_workfn(struct w percpu_ref_exit(&wb->refcnt); wb_exit(wb); + bdi_put(bdi); WARN_ON_ONCE(!list_empty(&wb->b_attached)); kfree_rcu(wb, rcu); } @@ -497,6 +492,7 @@ static int cgwb_create(struct backing_de INIT_LIST_HEAD(&wb->b_attached); INIT_WORK(&wb->release_work, cgwb_release_workfn); set_bit(WB_registered, &wb->state); + bdi_get(bdi); /* * The root wb determines the registered state of the whole bdi and @@ -528,6 +524,7 @@ static int cgwb_create(struct backing_de goto out_put; err_fprop_exit: + bdi_put(bdi); fprop_local_destroy_percpu(&wb->memcg_completions); err_ref_exit: percpu_ref_exit(&wb->refcnt); _
