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io_uring: stash ctx task reference for SQPOLL

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commit 2aede0e417 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>
This commit is contained in:
Jens Axboe
2020-10-12 11:15:07 -06:00
committed by Greg Kroah-Hartman
parent dd1acc182c
commit bf03059892
1 changed files with 29 additions and 10 deletions
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39
fs/io_uring.c
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@@ -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(struct io_ring_ctx *ctx,
{
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_ring_ctx *ctx,
{
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_ring_ctx *ctx,
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_ring_ctx *ctx)
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 entries, struct io_uring_params *p,
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;