This is a note to let you know that I've just added the patch titled
io_uring: stash ctx task reference for SQPOLL
to the 5.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
io_uring-stash-ctx-task-reference-for-sqpoll.patch
and it can be found in the queue-5.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Thu Oct 29 01:16:54 PM CET 2020
From: Jens Axboe <axboe@xxxxxxxxx>
Date: Mon, 12 Oct 2020 11:15:07 -0600
Subject: io_uring: stash ctx task reference for SQPOLL
From: Jens Axboe <axboe@xxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
Patches currently in stable-queue which might be from axboe@xxxxxxxxx are
queue-5.8/io_uring-convert-advanced-xarray-uses-to-the-normal-api.patch
queue-5.8/io_uring-don-t-run-task-work-on-an-exiting-task.patch
queue-5.8/io_uring-reference-nsproxy-for-file-table-commands.patch
queue-5.8/io_uring-stash-ctx-task-reference-for-sqpoll.patch
queue-5.8/io_uring-return-cancelation-status-from-poll-timeout-files-handlers.patch
queue-5.8/io_uring-fix-xarray-usage-in-io_uring_add_task_file.patch
queue-5.8/io_uring-fix-use-of-xarray-in-__io_uring_files_cancel.patch
queue-5.8/io-wq-fix-use-after-free-in-io_wq_worker_running.patch
queue-5.8/io_uring-don-t-rely-on-weak-files-references.patch
queue-5.8/io_uring-allow-timeout-poll-files-killing-to-take-task-into-account.patch
queue-5.8/io_uring-move-dropping-of-files-into-separate-helper.patch
queue-5.8/io_uring-unconditionally-grab-req-task.patch
queue-5.8/io_uring-enable-task-files-specific-overflow-flushing.patch
queue-5.8/io_wq-make-io_wqe-lock-a-raw_spinlock_t.patch
queue-5.8/io_uring-no-need-to-call-xa_destroy-on-empty-xarray.patch
