Commit d871198e authored by Jens Axboe's avatar Jens Axboe
Browse files

io_uring/fdinfo: grab ctx->uring_lock around io_uring_show_fdinfo() 



Not everything requires locking in there, which is why the 'has_lock'
variable exists. But enough does that it's a bit unwieldy to manage.
Wrap the whole thing in a ->uring_lock trylock, and just return
with no output if we fail to grab it. The existing trylock() will
already have greatly diminished utility/output for the failure case.

This fixes an issue with reading the SQE fields, if the ring is being
actively resized at the same time.

Reported-by: default avatarJann Horn <jannh@google.com>
Fixes: 79cfe9e5 ("io_uring/register: add IORING_REGISTER_RESIZE_RINGS")
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent f446c631

io_uring/fdinfo.c

+25 −23
Original line number Diff line number Diff line
@@ -86,13 +86,8 @@ static inline void napi_show_fdinfo(struct io_ring_ctx *ctx, 
}

#endif



/*

 * Caller holds a reference to the file already, we don't need to do

 * anything else to get an extra reference.

 */

__cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)

static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)

{

	struct io_ring_ctx *ctx = file->private_data;

	struct io_overflow_cqe *ocqe;

	struct io_rings *r = ctx->rings;

	struct rusage sq_usage;
@@ -106,7 +101,6 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file) 
	unsigned int sq_entries, cq_entries;

	int sq_pid = -1, sq_cpu = -1;

	u64 sq_total_time = 0, sq_work_time = 0;

	bool has_lock;

	unsigned int i;



	if (ctx->flags & IORING_SETUP_CQE32)
@@ -176,15 +170,7 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file) 
		seq_printf(m, "\n");

	}



	/*

	 * Avoid ABBA deadlock between the seq lock and the io_uring mutex,

	 * since fdinfo case grabs it in the opposite direction of normal use

	 * cases. If we fail to get the lock, we just don't iterate any

	 * structures that could be going away outside the io_uring mutex.

	 */

	has_lock = mutex_trylock(&ctx->uring_lock);



	if (has_lock && (ctx->flags & IORING_SETUP_SQPOLL)) {

	if (ctx->flags & IORING_SETUP_SQPOLL) {

		struct io_sq_data *sq = ctx->sq_data;



		/*
@@ -206,7 +192,7 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file) 
	seq_printf(m, "SqTotalTime:\t%llu\n", sq_total_time);

	seq_printf(m, "SqWorkTime:\t%llu\n", sq_work_time);

	seq_printf(m, "UserFiles:\t%u\n", ctx->file_table.data.nr);

	for (i = 0; has_lock && i < ctx->file_table.data.nr; i++) {

	for (i = 0; i < ctx->file_table.data.nr; i++) {

		struct file *f = NULL;



		if (ctx->file_table.data.nodes[i])
@@ -218,7 +204,7 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file) 
		}

	}

	seq_printf(m, "UserBufs:\t%u\n", ctx->buf_table.nr);

	for (i = 0; has_lock && i < ctx->buf_table.nr; i++) {

	for (i = 0; i < ctx->buf_table.nr; i++) {

		struct io_mapped_ubuf *buf = NULL;



		if (ctx->buf_table.nodes[i])
@@ -228,7 +214,7 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file) 
		else

			seq_printf(m, "%5u: <none>\n", i);

	}

	if (has_lock && !xa_empty(&ctx->personalities)) {

	if (!xa_empty(&ctx->personalities)) {

		unsigned long index;

		const struct cred *cred;
@@ -238,7 +224,7 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file) 
	}



	seq_puts(m, "PollList:\n");

	for (i = 0; has_lock && i < (1U << ctx->cancel_table.hash_bits); i++) {

	for (i = 0; i < (1U << ctx->cancel_table.hash_bits); i++) {

		struct io_hash_bucket *hb = &ctx->cancel_table.hbs[i];

		struct io_kiocb *req;
@@ -247,9 +233,6 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file) 
					task_work_pending(req->tctx->task));

	}



	if (has_lock)

		mutex_unlock(&ctx->uring_lock);



	seq_puts(m, "CqOverflowList:\n");

	spin_lock(&ctx->completion_lock);

	list_for_each_entry(ocqe, &ctx->cq_overflow_list, list) {
@@ -262,4 +245,23 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file) 
	spin_unlock(&ctx->completion_lock);

	napi_show_fdinfo(ctx, m);

}



/*

 * Caller holds a reference to the file already, we don't need to do

 * anything else to get an extra reference.

 */

__cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)

{

	struct io_ring_ctx *ctx = file->private_data;



	/*

	 * Avoid ABBA deadlock between the seq lock and the io_uring mutex,

	 * since fdinfo case grabs it in the opposite direction of normal use

	 * cases.

	 */

	if (mutex_trylock(&ctx->uring_lock)) {

		__io_uring_show_fdinfo(ctx, m);

		mutex_unlock(&ctx->uring_lock);

	}

}

#endif