io_uring/fdinfo: be a bit nicer when looping a lot of SQEs/CQEs

Add cond_resched() in those dump loops, just in case a lot of entries
are being dumped. And detect invalid CQ ring head/tail entries, to avoid
iterating more than what is necessary. Generally not an issue, but can be
if things like KASAN or other debugging metrics are enabled.

Reported-by: 是参差 <[email protected]>
Link: https://lore.kernel.org/all/PS1PPF7E1D7501FE5631002D242DD89403FAB9BA@PS1PPF7E1D7501F.apcprd02.prod.outlook.com/
Reviewed-by: Keith Busch <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: axboe

io_uring/fdinfo.c

@@ -67,7 +67,7 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 	unsigned int cq_head = READ_ONCE(r->cq.head);
 	unsigned int cq_tail = READ_ONCE(r->cq.tail);
 	unsigned int sq_shift = 0;
-	unsigned int sq_entries;
+	unsigned int cq_entries, sq_entries;
 	int sq_pid = -1, sq_cpu = -1;
 	u64 sq_total_time = 0, sq_work_time = 0;
 	unsigned int i;
@@ -146,9 +146,11 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 			}
 		}
 		seq_printf(m, "\n");
+		cond_resched();
 	}
 	seq_printf(m, "CQEs:\t%u\n", cq_tail - cq_head);
-	while (cq_head < cq_tail) {
+	cq_entries = min(cq_tail - cq_head, ctx->cq_entries);
+	for (i = 0; i < cq_entries; i++) {
 		struct io_uring_cqe *cqe;
 		bool cqe32 = false;
 
@@ -163,8 +165,11 @@ static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
 					cqe->big_cqe[0], cqe->big_cqe[1]);
 		seq_printf(m, "\n");
 		cq_head++;
-		if (cqe32)
+		if (cqe32) {
 			cq_head++;
+			i++;
+		}
+		cond_resched();
 	}
 
 	if (ctx->flags & IORING_SETUP_SQPOLL) {