From: Jens Axboe axboe@kernel.dk
commit 2aede0e417db846793c276c7a1bbf7262c8349b0 upstream.
We can grab a reference to the task instead of stashing away the task files_struct. This is doable without creating a circular reference between the ring fd and the task itself.
Reviewed-by: Pavel Begunkov asml.silence@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/io_uring.c | 39 +++++++++++++++++++++++++++++---------- 1 file changed, 29 insertions(+), 10 deletions(-)
--- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -264,7 +264,16 @@ struct io_ring_ctx { /* IO offload */ struct io_wq *io_wq; struct task_struct *sqo_thread; /* if using sq thread polling */ - struct mm_struct *sqo_mm; + + /* + * For SQPOLL usage - we hold a reference to the parent task, so we + * have access to the ->files + */ + struct task_struct *sqo_task; + + /* Only used for accounting purposes */ + struct mm_struct *mm_account; + wait_queue_head_t sqo_wait;
/* @@ -4421,9 +4430,10 @@ static int io_sq_thread_acquire_mm(struc { if (io_op_defs[req->opcode].needs_mm && !current->mm) { if (unlikely(!(ctx->flags & IORING_SETUP_SQPOLL) || - !mmget_not_zero(ctx->sqo_mm))) + !ctx->sqo_task->mm || + !mmget_not_zero(ctx->sqo_task->mm))) return -EFAULT; - kthread_use_mm(ctx->sqo_mm); + kthread_use_mm(ctx->sqo_task->mm); }
return 0; @@ -7104,9 +7114,6 @@ static int io_sq_offload_start(struct io { int ret;
- mmgrab(current->mm); - ctx->sqo_mm = current->mm; - if (ctx->flags & IORING_SETUP_SQPOLL) { ret = -EPERM; if (!capable(CAP_SYS_ADMIN)) @@ -7151,8 +7158,6 @@ static int io_sq_offload_start(struct io return 0; err: io_finish_async(ctx); - mmdrop(ctx->sqo_mm); - ctx->sqo_mm = NULL; return ret; }
@@ -7482,8 +7487,12 @@ static void io_destroy_buffers(struct io static void io_ring_ctx_free(struct io_ring_ctx *ctx) { io_finish_async(ctx); - if (ctx->sqo_mm) - mmdrop(ctx->sqo_mm); + if (ctx->sqo_task) { + put_task_struct(ctx->sqo_task); + ctx->sqo_task = NULL; + mmdrop(ctx->mm_account); + ctx->mm_account = NULL; + }
io_iopoll_reap_events(ctx); io_sqe_buffer_unregister(ctx); @@ -8256,6 +8265,16 @@ static int io_uring_create(unsigned entr ctx->user = user; ctx->creds = get_current_cred();
+ ctx->sqo_task = get_task_struct(current); + /* + * This is just grabbed for accounting purposes. When a process exits, + * the mm is exited and dropped before the files, hence we need to hang + * on to this mm purely for the purposes of being able to unaccount + * memory (locked/pinned vm). It's not used for anything else. + */ + mmgrab(current->mm); + ctx->mm_account = current->mm; + ret = io_allocate_scq_urings(ctx, p); if (ret) goto err;