6.1-stable review patch. If anyone has any objections, please let me know.
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From: Jens Axboe axboe@kernel.dk
[ Upstream commit f024d3a8ded0d8d2129ae123d7a5305c29ca44ce ]
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the CQ or SQ tail/head entries are known racy in that they are just a view into that very instant and may of course be outdated by the time they are reported.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.co... Reported-by: syzbot+3e77fd302e99f5af9394@syzkaller.appspotmail.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- io_uring/fdinfo.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c index ea2c2ded4e412..4a50531699777 100644 --- a/io_uring/fdinfo.c +++ b/io_uring/fdinfo.c @@ -79,11 +79,11 @@ static __cold void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, 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++) {