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io_uring: acquire 'mm' for task_work for SQPOLL

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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>
This commit is contained in:
Jens Axboe 2020-06-16 18:42:49 -06:00
parent bbde017a32
commit 9d8426a091
1 changed files with 29 additions and 15 deletions
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44
fs/io_uring.c
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@ -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 @@ fail_req:
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;