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From:   Pavel Begunkov <asml.silence@gmail.com>
To:     Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH 5.9] io_uring: fix NULL-mm for linked reqs
Date:   Thu, 25 Jun 2020 12:38:13 +0300
Message-Id: <f7d8272bcf142fe2c11c85ecd86f7f75f6e48316.1593077850.git.asml.silence@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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__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 <asml.silence@gmail.com>
---
 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