From cccf0ee834559ae0b327b40290e14f6a2a017177 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 27 Jan 2020 16:34:48 -0700 Subject: io_uring/io-wq: don't use static creds/mm assignments We currently setup the io_wq with a static set of mm and creds. Even for a single-use io-wq per io_uring, this is suboptimal as we have may have multiple enters of the ring. For sharing the io-wq backend, it doesn't work at all. Switch to passing in the creds and mm when the work item is setup. This means that async work is no longer deferred to the io_uring mm and creds, it is done with the current mm and creds. Flag this behavior with IORING_FEAT_CUR_PERSONALITY, so applications know they can rely on the current personality (mm and creds) being the same for direct issue and async issue. Reviewed-by: Stefan Metzmacher Signed-off-by: Jens Axboe --- fs/io-wq.c | 68 ++++++++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 46 insertions(+), 22 deletions(-) (limited to 'fs/io-wq.c') diff --git a/fs/io-wq.c b/fs/io-wq.c index 54e270ae12ab..7ccedc82a703 100644 --- a/fs/io-wq.c +++ b/fs/io-wq.c @@ -56,7 +56,8 @@ struct io_worker { struct rcu_head rcu; struct mm_struct *mm; - const struct cred *creds; + const struct cred *cur_creds; + const struct cred *saved_creds; struct files_struct *restore_files; }; @@ -109,8 +110,6 @@ struct io_wq { struct task_struct *manager; struct user_struct *user; - const struct cred *creds; - struct mm_struct *mm; refcount_t refs; struct completion done; @@ -137,9 +136,9 @@ static bool __io_worker_unuse(struct io_wqe *wqe, struct io_worker *worker) { bool dropped_lock = false; - if (worker->creds) { - revert_creds(worker->creds); - worker->creds = NULL; + if (worker->saved_creds) { + revert_creds(worker->saved_creds); + worker->cur_creds = worker->saved_creds = NULL; } if (current->files != worker->restore_files) { @@ -398,6 +397,43 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe, unsigned *hash) return NULL; } +static void io_wq_switch_mm(struct io_worker *worker, struct io_wq_work *work) +{ + if (worker->mm) { + unuse_mm(worker->mm); + mmput(worker->mm); + worker->mm = NULL; + } + if (!work->mm) { + set_fs(KERNEL_DS); + return; + } + if (mmget_not_zero(work->mm)) { + use_mm(work->mm); + if (!worker->mm) + set_fs(USER_DS); + worker->mm = work->mm; + /* hang on to this mm */ + work->mm = NULL; + return; + } + + /* failed grabbing mm, ensure work gets cancelled */ + work->flags |= IO_WQ_WORK_CANCEL; +} + +static void io_wq_switch_creds(struct io_worker *worker, + struct io_wq_work *work) +{ + const struct cred *old_creds = override_creds(work->creds); + + worker->cur_creds = work->creds; + if (worker->saved_creds) + put_cred(old_creds); /* creds set by previous switch */ + else + worker->saved_creds = old_creds; +} + static void io_worker_handle_work(struct io_worker *worker) __releases(wqe->lock) { @@ -446,18 +482,10 @@ next: current->files = work->files; task_unlock(current); } - if ((work->flags & IO_WQ_WORK_NEEDS_USER) && !worker->mm && - wq->mm) { - if (mmget_not_zero(wq->mm)) { - use_mm(wq->mm); - set_fs(USER_DS); - worker->mm = wq->mm; - } else { - work->flags |= IO_WQ_WORK_CANCEL; - } - } - if (!worker->creds) - worker->creds = override_creds(wq->creds); + if (work->mm != worker->mm) + io_wq_switch_mm(worker, work); + if (worker->cur_creds != work->creds) + io_wq_switch_creds(worker, work); /* * OK to set IO_WQ_WORK_CANCEL even for uncancellable work, * the worker function will do the right thing. @@ -1037,7 +1065,6 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data) /* caller must already hold a reference to this */ wq->user = data->user; - wq->creds = data->creds; for_each_node(node) { struct io_wqe *wqe; @@ -1064,9 +1091,6 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data) init_completion(&wq->done); - /* caller must have already done mmgrab() on this mm */ - wq->mm = data->mm; - wq->manager = kthread_create(io_wq_manager, wq, "io_wq_manager"); if (!IS_ERR(wq->manager)) { wake_up_process(wq->manager); -- cgit v1.2.3