linux-kernel - [PATCH v2 2/2] io_uring: Improve exception handling in io_ring_ctx

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Date: Wed, 10 Jan 2024 21:50:15 +0100
From: Markus Elfring <Markus.Elfring@....de>
To: io-uring@...r.kernel.org, kernel-janitors@...r.kernel.org,
 Gabriel Krisman Bertazi <krisman@...e.de>, Jens Axboe <axboe@...nel.dk>,
 Pavel Begunkov <asml.silence@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 2/2] io_uring: Improve exception handling in
 io_ring_ctx_alloc()

From: Markus Elfring <elfring@...rs.sourceforge.net>
Date: Wed, 10 Jan 2024 21:15:48 +0100

The label “err” was used to jump to a kfree() call despite of
the detail in the implementation of the function “io_ring_ctx_alloc”
that it was determined already that a corresponding variable contained
a null pointer because of a failed memory allocation.

1. Thus use more appropriate labels instead.

2. Reorder jump targets at the end.

Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
---

See also:
https://wiki.sei.cmu.edu/confluence/display/c/MEM12-C.+Consider+using+a+goto+chain+when+leaving+a+function+on+error+when+using+and+releasing+resources


 io_uring/io_uring.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index c9a63c39cdd0..7727cdd505ae 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -295,12 +295,14 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	hash_bits = ilog2(p->cq_entries) - 5;
 	hash_bits = clamp(hash_bits, 1, 8);
 	if (io_alloc_hash_table(&ctx->cancel_table, hash_bits))
-		goto err;
+		goto destroy_io_bl_xa;
+
 	if (io_alloc_hash_table(&ctx->cancel_table_locked, hash_bits))
-		goto err;
+		goto free_cancel_table_hbs;
+
 	if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free,
 			    0, GFP_KERNEL))
-		goto err;
+		goto free_cancel_table_locked_hbs;

 	ctx->flags = p->flags;
 	init_waitqueue_head(&ctx->sqo_sq_wait);
@@ -341,9 +343,12 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	INIT_WQ_LIST(&ctx->submit_state.compl_reqs);
 	INIT_HLIST_HEAD(&ctx->cancelable_uring_cmd);
 	return ctx;
-err:
-	kfree(ctx->cancel_table.hbs);
+
+free_cancel_table_locked_hbs:
 	kfree(ctx->cancel_table_locked.hbs);
+free_cancel_table_hbs:
+	kfree(ctx->cancel_table.hbs);
+destroy_io_bl_xa:
 	xa_destroy(&ctx->io_bl_xa);
 	kfree(ctx);
 	return NULL;
--
2.43.0