The patch below does not apply to the 5.7-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9d8426a09195e2dcf2aa249de2aaadd792d491c7 Mon Sep 17 00:00:00 2001

From: Jens Axboe axboe@kernel.dk Date: Tue, 16 Jun 2020 18:42:49 -0600 Subject: [PATCH] io_uring: acquire 'mm' for task_work for SQPOLL

If we're unlucky with timing, we could be running task_work after having dropped the memory context in the sq thread. Since dropping the context requires a runnable task state, we cannot reliably drop it as part of our check-for-work loop in io_sq_thread(). Instead, abstract out the mm acquire for the sq thread into a helper, and call it from the async task work handler.

Cc: stable@vger.kernel.org # v5.7 Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/fs/io_uring.c b/fs/io_uring.c index 9d2ae9aa8b45..98c83fbf4f88 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -4256,6 +4256,28 @@ static void io_async_queue_proc(struct file *file, struct wait_queue_head *head, __io_queue_proc(&pt->req->apoll->poll, pt, head); }

+static void io_sq_thread_drop_mm(struct io_ring_ctx *ctx) +{ + struct mm_struct *mm = current->mm; + + if (mm) { + kthread_unuse_mm(mm); + mmput(mm); + } +} + +static int io_sq_thread_acquire_mm(struct io_ring_ctx *ctx, + struct io_kiocb *req) +{ + if (io_op_defs[req->opcode].needs_mm && !current->mm) { + if (unlikely(!mmget_not_zero(ctx->sqo_mm))) + return -EFAULT; + kthread_use_mm(ctx->sqo_mm); + } + + return 0; +} + static void io_async_task_func(struct callback_head *cb) { struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); @@ -4290,11 +4312,16 @@ static void io_async_task_func(struct callback_head *cb)

if (!canceled) { __set_current_state(TASK_RUNNING); + if (io_sq_thread_acquire_mm(ctx, req)) { + io_cqring_add_event(req, -EFAULT); + goto end_req; + } mutex_lock(&ctx->uring_lock); __io_queue_sqe(req, NULL); mutex_unlock(&ctx->uring_lock); } else { io_cqring_ev_posted(ctx); +end_req: req_set_fail_links(req); io_double_put_req(req); } @@ -5841,11 +5868,8 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req, if (unlikely(req->opcode >= IORING_OP_LAST)) return -EINVAL;

- if (io_op_defs[req->opcode].needs_mm && !current->mm) { - if (unlikely(!mmget_not_zero(ctx->sqo_mm))) - return -EFAULT; - kthread_use_mm(ctx->sqo_mm); - } + if (unlikely(io_sq_thread_acquire_mm(ctx, req))) + return -EFAULT;

sqe_flags = READ_ONCE(sqe->flags); /* enforce forwards compatibility on users */ @@ -5954,16 +5978,6 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr, return submitted; }

-static inline void io_sq_thread_drop_mm(struct io_ring_ctx *ctx) -{ - struct mm_struct *mm = current->mm; - - if (mm) { - kthread_unuse_mm(mm); - mmput(mm); - } -} - static int io_sq_thread(void *data) { struct io_ring_ctx *ctx = data;