[PATCH] io_uring/fdinfo: annotate racy sq/cq head/tail reads

[PATCH] io_uring/fdinfo: annotate racy sq/cq head/tail reads

[Jens Axboe]

syzbot complains about the cached sq head read, and it's totally right.
But we don't need to care, it's just reading fdinfo, and reading the
CQ or SQ tail/head entries are known racy in that they are just a view
into that very instant and may of course be outdated by the time they
are reported.

Annotate both the SQ head and CQ tail read with data_race() to avoid
this syzbot complaint.

Link: https://lore.kernel.org/io-uring/6811f6dc.050a0220.39e3a1.0d0e.GAE@google.com/
Reported-by: syzbot+3e77fd302e99f5af9394@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c
index f60d0a9d505e..9414ca6d101c 100644
--- a/io_uring/fdinfo.c
+++ b/io_uring/fdinfo.c
@@ -123,11 +123,11 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)
 	seq_printf(m, "SqMask:\t0x%x\n", sq_mask);
 	seq_printf(m, "SqHead:\t%u\n", sq_head);
 	seq_printf(m, "SqTail:\t%u\n", sq_tail);
-	seq_printf(m, "CachedSqHead:\t%u\n", ctx->cached_sq_head);
+	seq_printf(m, "CachedSqHead:\t%u\n", data_race(ctx->cached_sq_head));
 	seq_printf(m, "CqMask:\t0x%x\n", cq_mask);
 	seq_printf(m, "CqHead:\t%u\n", cq_head);
 	seq_printf(m, "CqTail:\t%u\n", cq_tail);
-	seq_printf(m, "CachedCqTail:\t%u\n", ctx->cached_cq_tail);
+	seq_printf(m, "CachedCqTail:\t%u\n", data_race(ctx->cached_cq_tail));
 	seq_printf(m, "SQEs:\t%u\n", sq_tail - sq_head);
 	sq_entries = min(sq_tail - sq_head, ctx->sq_entries);
 	for (i = 0; i < sq_entries; i++) {

-- 
Jens Axboe