From: Shenghui Wang <shhuiw@foxmail.com> mainline inclusion from mainline-5.0-rc1 commit f383ae300c4b6466824fd5c8cbd0a6c4ed2b53d3 category: backport "echo 1 > writeback_running" marks writeback_running even if no writeback kthread created as "d_strtoul(writeback_running)" will simply set dc-> writeback_running without checking the existence of dc->writeback_thread. Add check for setting writeback_running via sysfs: if no writeback kthread available, reject setting to 1. v2 -> v3: * Make message on wrong assignment more clear. * Print name of bcache device instead of name of backing device. Signed-off-by: Shenghui Wang <shhuiw@foxmail.com> Signed-off-by: Coly Li <colyli@suse.de> Signed-off-by: Jens Axboe <axboe@kernel.dk> --- drivers/md/bcache/sysfs.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c index 2bc4d90a2d0b..419939c39fd9 100644 --- a/drivers/md/bcache/sysfs.c +++ b/drivers/md/bcache/sysfs.c @@ -392,8 +392,25 @@ STORE(bch_cached_dev) mutex_lock(&bch_register_lock); size = __cached_dev_store(kobj, attr, buf, size); - if (attr == &sysfs_writeback_running) - bch_writeback_queue(dc); + if (attr == &sysfs_writeback_running) { + /* dc->writeback_running changed in __cached_dev_store() */ + if (IS_ERR_OR_NULL(dc->writeback_thread)) { + /* + * reject setting it to 1 via sysfs if writeback + * kthread is not created yet. + */ + if (dc->writeback_running) { + dc->writeback_running = false; + pr_err("%s: failed to run non-existent writeback thread", + dc->disk.disk->disk_name); + } + } else + /* + * writeback kthread will check if dc->writeback_running + * is true or false. + */ + bch_writeback_queue(dc); + } /* * Only set BCACHE_DEV_WB_RUNNING when cached device attached to -- 2.16.4