On 8/10/20 9:37 AM, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 449dc8c9 Merge tag 'for-v5.9' of git://git.kernel.org/pub/.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=11293dc6900000 > kernel config: https://syzkaller.appspot.com/x/.config?x=9d25235bf0162fbc > dashboard link: https://syzkaller.appspot.com/bug?extid=ef4b654b49ed7ff049bf > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=126b0f1a900000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13e32994900000 > > The issue was bisected to: > > commit e62753e4e2926f249d088cc0517be5ed4efec6d6 > Author: Bijan Mottahedeh <bijan.mottahedeh@xxxxxxxxxx> > Date: Sat May 23 04:31:18 2020 +0000 > > io_uring: call statx directly I don't think this one is to blame, it's a generic issue with needing to put the file table from the error/fail path. Something like the below should fix it - if we have the completion lock locked, then punt the file table put to a safe context through task_work instead. Looks bigger than it is, due to moving some of the generic task_work handling functions up a bit. diff --git a/fs/io_uring.c b/fs/io_uring.c index f9be665d1c5e..5df805d6251e 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -1108,10 +1108,16 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx) } } -static void io_req_clean_work(struct io_kiocb *req) +/* + * Returns true if we need to defer file table putting. This can only happen + * from the error path with REQ_F_COMP_LOCKED set. + */ +static bool io_req_clean_work(struct io_kiocb *req) { if (!(req->flags & REQ_F_WORK_INITIALIZED)) - return; + return false; + + req->flags &= ~REQ_F_WORK_INITIALIZED; if (req->work.mm) { mmdrop(req->work.mm); @@ -1124,6 +1130,9 @@ static void io_req_clean_work(struct io_kiocb *req) if (req->work.fs) { struct fs_struct *fs = req->work.fs; + if (req->flags & REQ_F_COMP_LOCKED) + return true; + spin_lock(&req->work.fs->lock); if (--fs->users) fs = NULL; @@ -1132,7 +1141,8 @@ static void io_req_clean_work(struct io_kiocb *req) free_fs_struct(fs); req->work.fs = NULL; } - req->flags &= ~REQ_F_WORK_INITIALIZED; + + return false; } static void io_prep_async_work(struct io_kiocb *req) @@ -1544,7 +1554,7 @@ static inline void io_put_file(struct io_kiocb *req, struct file *file, fput(file); } -static void io_dismantle_req(struct io_kiocb *req) +static bool io_dismantle_req(struct io_kiocb *req) { io_clean_op(req); @@ -1552,7 +1562,6 @@ static void io_dismantle_req(struct io_kiocb *req) kfree(req->io); if (req->file) io_put_file(req, req->file, (req->flags & REQ_F_FIXED_FILE)); - io_req_clean_work(req); if (req->flags & REQ_F_INFLIGHT) { struct io_ring_ctx *ctx = req->ctx; @@ -1564,15 +1573,108 @@ static void io_dismantle_req(struct io_kiocb *req) wake_up(&ctx->inflight_wait); spin_unlock_irqrestore(&ctx->inflight_lock, flags); } + + return io_req_clean_work(req); } -static void __io_free_req(struct io_kiocb *req) +static void __io_req_task_cancel(struct io_kiocb *req, int error) { - struct io_ring_ctx *ctx; + struct io_ring_ctx *ctx = req->ctx; + + spin_lock_irq(&ctx->completion_lock); + io_cqring_fill_event(req, error); + io_commit_cqring(ctx); + spin_unlock_irq(&ctx->completion_lock); + + io_cqring_ev_posted(ctx); + req_set_fail_links(req); + io_double_put_req(req); +} + +static void io_req_task_cancel(struct callback_head *cb) +{ + struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); + + __io_req_task_cancel(req, -ECANCELED); +} + +static int io_req_task_work_add(struct io_kiocb *req, struct callback_head *cb) +{ + struct task_struct *tsk = req->task; + struct io_ring_ctx *ctx = req->ctx; + int ret, notify = TWA_RESUME; + + ret = __task_work_add(tsk, cb); + if (unlikely(ret)) + return ret; + + /* + * SQPOLL kernel thread doesn't need notification, just a wakeup. + * For any other work, use signaled wakeups if the task isn't + * running to avoid dependencies between tasks or threads. If + * the issuing task is currently waiting in the kernel on a thread, + * and same thread is waiting for a completion event, then we need + * to ensure that the issuing task processes task_work. TWA_SIGNAL + * is needed for that. + */ + if (ctx->flags & IORING_SETUP_SQPOLL) + notify = 0; + else if (READ_ONCE(tsk->state) != TASK_RUNNING) + notify = TWA_SIGNAL; + + __task_work_notify(tsk, notify); + wake_up_process(tsk); + return 0; +} + +static void __io_req_task_submit(struct io_kiocb *req) +{ + struct io_ring_ctx *ctx = req->ctx; + + if (!__io_sq_thread_acquire_mm(ctx)) { + mutex_lock(&ctx->uring_lock); + __io_queue_sqe(req, NULL, NULL); + mutex_unlock(&ctx->uring_lock); + } else { + __io_req_task_cancel(req, -EFAULT); + } +} + +static void io_req_task_submit(struct callback_head *cb) +{ + struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); + + __io_req_task_submit(req); +} + + +static void __io_req_task_queue(struct io_kiocb *req, task_work_func_t func) +{ + int ret; + + init_task_work(&req->task_work, func); + + ret = io_req_task_work_add(req, &req->task_work); + if (unlikely(ret)) { + struct task_struct *tsk; + + init_task_work(&req->task_work, io_req_task_cancel); + tsk = io_wq_get_task(req->ctx->io_wq); + task_work_add(tsk, &req->task_work, 0); + wake_up_process(tsk); + } +} + +static void io_req_task_queue(struct io_kiocb *req) +{ + __io_req_task_queue(req, io_req_task_submit); +} + +static void __io_free_req_finish(struct io_kiocb *req) +{ + struct io_ring_ctx *ctx = req->ctx; - io_dismantle_req(req); __io_put_req_task(req); - ctx = req->ctx; if (likely(!io_is_fallback_req(req))) kmem_cache_free(req_cachep, req); else @@ -1580,6 +1682,29 @@ static void __io_free_req(struct io_kiocb *req) percpu_ref_put(&ctx->refs); } +static void io_req_task_file_table_put(struct callback_head *cb) +{ + struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); + struct fs_struct *fs = req->work.fs; + + spin_lock(&req->work.fs->lock); + if (--fs->users) + fs = NULL; + spin_unlock(&req->work.fs->lock); + if (fs) + free_fs_struct(fs); + req->work.fs = NULL; + __io_free_req_finish(req); +} + +static void __io_free_req(struct io_kiocb *req) +{ + if (!io_dismantle_req(req)) + __io_free_req_finish(req); + else + __io_req_task_queue(req, io_req_task_file_table_put); +} + static bool io_link_cancel_timeout(struct io_kiocb *req) { struct io_ring_ctx *ctx = req->ctx; @@ -1667,6 +1792,7 @@ static void __io_fail_links(struct io_kiocb *req) trace_io_uring_fail_link(req, link); io_cqring_fill_event(link, -ECANCELED); + link->flags |= REQ_F_COMP_LOCKED; __io_double_put_req(link); req->flags &= ~REQ_F_LINK_TIMEOUT; } @@ -1717,93 +1843,6 @@ static struct io_kiocb *io_req_find_next(struct io_kiocb *req) return __io_req_find_next(req); } -static int io_req_task_work_add(struct io_kiocb *req, struct callback_head *cb) -{ - struct task_struct *tsk = req->task; - struct io_ring_ctx *ctx = req->ctx; - int ret, notify = TWA_RESUME; - - ret = __task_work_add(tsk, cb); - if (unlikely(ret)) - return ret; - - /* - * SQPOLL kernel thread doesn't need notification, just a wakeup. - * For any other work, use signaled wakeups if the task isn't - * running to avoid dependencies between tasks or threads. If - * the issuing task is currently waiting in the kernel on a thread, - * and same thread is waiting for a completion event, then we need - * to ensure that the issuing task processes task_work. TWA_SIGNAL - * is needed for that. - */ - if (ctx->flags & IORING_SETUP_SQPOLL) - notify = 0; - else if (READ_ONCE(tsk->state) != TASK_RUNNING) - notify = TWA_SIGNAL; - - __task_work_notify(tsk, notify); - wake_up_process(tsk); - return 0; -} - -static void __io_req_task_cancel(struct io_kiocb *req, int error) -{ - struct io_ring_ctx *ctx = req->ctx; - - spin_lock_irq(&ctx->completion_lock); - io_cqring_fill_event(req, error); - io_commit_cqring(ctx); - spin_unlock_irq(&ctx->completion_lock); - - io_cqring_ev_posted(ctx); - req_set_fail_links(req); - io_double_put_req(req); -} - -static void io_req_task_cancel(struct callback_head *cb) -{ - struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); - - __io_req_task_cancel(req, -ECANCELED); -} - -static void __io_req_task_submit(struct io_kiocb *req) -{ - struct io_ring_ctx *ctx = req->ctx; - - if (!__io_sq_thread_acquire_mm(ctx)) { - mutex_lock(&ctx->uring_lock); - __io_queue_sqe(req, NULL, NULL); - mutex_unlock(&ctx->uring_lock); - } else { - __io_req_task_cancel(req, -EFAULT); - } -} - -static void io_req_task_submit(struct callback_head *cb) -{ - struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); - - __io_req_task_submit(req); -} - -static void io_req_task_queue(struct io_kiocb *req) -{ - int ret; - - init_task_work(&req->task_work, io_req_task_submit); - - ret = io_req_task_work_add(req, &req->task_work); - if (unlikely(ret)) { - struct task_struct *tsk; - - init_task_work(&req->task_work, io_req_task_cancel); - tsk = io_wq_get_task(req->ctx->io_wq); - task_work_add(tsk, &req->task_work, 0); - wake_up_process(tsk); - } -} - static void io_queue_next(struct io_kiocb *req) { struct io_kiocb *nxt = io_req_find_next(req); @@ -1872,7 +1911,7 @@ static void io_req_free_batch(struct req_batch *rb, struct io_kiocb *req) req->flags &= ~REQ_F_TASK_PINNED; } - io_dismantle_req(req); + WARN_ON_ONCE(io_dismantle_req(req)); rb->reqs[rb->to_free++] = req; if (unlikely(rb->to_free == ARRAY_SIZE(rb->reqs))) __io_req_free_batch_flush(req->ctx, rb); -- Jens Axboe
