2020-06-25 10:01:36

by Pavel Begunkov

Subject: [PATCH 5.9] io_uring: fix NULL-mm for linked reqs

__io_queue_sqe() tries to handle all request of a link,
so it's not enough to grab mm in io_sq_thread_acquire_mm()
based just on the head.

Don't check req->needs_mm and do it always.

Signed-off-by: Pavel Begunkov <[email protected]>
---
fs/io_uring.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 21bc86670c56..e7b1e696fecd 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2000,10 +2000,9 @@ static void io_sq_thread_drop_mm(struct io_ring_ctx *ctx)
}
}

-static int io_sq_thread_acquire_mm(struct io_ring_ctx *ctx,
- struct io_kiocb *req)
+static int __io_sq_thread_acquire_mm(struct io_ring_ctx *ctx)
{
- if (io_op_defs[req->opcode].needs_mm && !current->mm) {
+ if (!current->mm) {
if (unlikely(!mmget_not_zero(ctx->sqo_mm)))
return -EFAULT;
kthread_use_mm(ctx->sqo_mm);
@@ -2012,6 +2011,14 @@ static int io_sq_thread_acquire_mm(struct io_ring_ctx *ctx,
return 0;
}

+static int io_sq_thread_acquire_mm(struct io_ring_ctx *ctx,
+ struct io_kiocb *req)
+{
+ if (!io_op_defs[req->opcode].needs_mm)
+ return 0;
+ return __io_sq_thread_acquire_mm(ctx);
+}
+
#ifdef CONFIG_BLOCK
static bool io_resubmit_prep(struct io_kiocb *req, int error)
{
@@ -2788,7 +2795,7 @@ static void io_async_buf_retry(struct callback_head *cb)
ctx = req->ctx;

__set_current_state(TASK_RUNNING);
- if (!io_sq_thread_acquire_mm(ctx, req)) {
+ if (!__io_sq_thread_acquire_mm(ctx)) {
mutex_lock(&ctx->uring_lock);
__io_queue_sqe(req, NULL);
mutex_unlock(&ctx->uring_lock);
--
2.24.0

2020-06-25 13:28:11

by Jens Axboe

Subject: Re: [PATCH 5.9] io_uring: fix NULL-mm for linked reqs

On 6/25/20 3:38 AM, Pavel Begunkov wrote:
> __io_queue_sqe() tries to handle all request of a link,
> so it's not enough to grab mm in io_sq_thread_acquire_mm()
> based just on the head.
>
> Don't check req->needs_mm and do it always.

Applied, thanks.

--
Jens Axboe