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io_uring: stash ctx task reference for SQPOLL

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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>
This commit is contained in:
Jens Axboe 2020-09-14 10:45:53 -06:00
parent f573d38445
commit 2aede0e417
1 changed files with 34 additions and 13 deletions
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47
fs/io_uring.c
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@ -265,7 +265,16 @@ 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;
/*
@ -969,9 +978,10 @@ static int __io_sq_thread_acquire_mm(struct io_ring_ctx *ctx)
{
if (!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;
@ -7591,11 +7601,11 @@ static void io_unaccount_mem(struct io_ring_ctx *ctx, unsigned long nr_pages,
if (ctx->limit_mem)
__io_unaccount_mem(ctx->user, nr_pages);
if (ctx->sqo_mm) {
if (ctx->mm_account) {
if (acct == ACCT_LOCKED)
ctx->sqo_mm->locked_vm -= nr_pages;
ctx->mm_account->locked_vm -= nr_pages;
else if (acct == ACCT_PINNED)
atomic64_sub(nr_pages, &ctx->sqo_mm->pinned_vm);
atomic64_sub(nr_pages, &ctx->mm_account->pinned_vm);
}
}
@ -7610,11 +7620,11 @@ static int io_account_mem(struct io_ring_ctx *ctx, unsigned long nr_pages,
return ret;
}
if (ctx->sqo_mm) {
if (ctx->mm_account) {
if (acct == ACCT_LOCKED)
ctx->sqo_mm->locked_vm += nr_pages;
ctx->mm_account->locked_vm += nr_pages;
else if (acct == ACCT_PINNED)
atomic64_add(nr_pages, &ctx->sqo_mm->pinned_vm);
atomic64_add(nr_pages, &ctx->mm_account->pinned_vm);
}
return 0;
@ -7918,9 +7928,12 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
{
io_finish_async(ctx);
io_sqe_buffer_unregister(ctx);
if (ctx->sqo_mm) {
mmdrop(ctx->sqo_mm);
ctx->sqo_mm = NULL;
if (ctx->sqo_task) {
put_task_struct(ctx->sqo_task);
ctx->sqo_task = NULL;
mmdrop(ctx->mm_account);
ctx->mm_account = NULL;
}
io_sqe_files_unregister(ctx);
@ -8665,8 +8678,16 @@ 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->sqo_mm = current->mm;
ctx->mm_account = current->mm;
/*
* Account memory _before_ installing the file descriptor. Once