On 1/9/20 7:26 AM, Pavel Begunkov wrote:
> On 1/9/2020 4:17 PM, Dmitrii Dolgov wrote:
>> With combination of --fixedbufs and an old version of fio I've managed
>> to get a strange situation, when doing io_iopoll_complete NULL pointer
>> dereference on file_data was caused in io_free_req_many. Interesting
>> enough, the very same configuration doesn't fail on a newest version of
>> fio (the old one is fc220349e4514, the new one is 2198a6b5a9f4), but I
>> guess it still makes sense to have this check if it's possible to craft
>> such request to io_uring.
>
> I didn't looked up why it could become NULL in the first place, but the
> problem is probably deeper.
>
> 1. I don't see why it puts @rb->to_free @file_data->refs, even though
> there could be non-fixed reqs. It needs to count REQ_F_FIXED_FILE reqs
> and put only as much.
Agree on the fixed file refs, there's a bug there where it assumes they
are all still fixed. See below - Dmitrii, use this patch for testing
instead of the other one!
> 2. Jens, there is another line bothering me, could you take a look?
>
> io_free_req_many()
> {
> ...
> if (req->flags & REQ_F_INFLIGHT) ...;
> else
> rb->reqs[i] = NULL;
> ...
> }
>
> It zeroes rb->reqs[i], calls __io_req_aux_free(), but did not free
> memory for the request itself. Is it as intended?
We free them at the end of that function, in bulk. But we can't do that
with the aux data.
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 32aee149f652..b5dcf6c800ef 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1218,6 +1218,8 @@ struct req_batch {
static void io_free_req_many(struct io_ring_ctx *ctx, struct req_batch *rb)
{
+ int fixed_refs = 0;
+
if (!rb->to_free)
return;
if (rb->need_iter) {
@@ -1227,8 +1229,10 @@ static void io_free_req_many(struct io_ring_ctx *ctx, struct req_batch *rb)
for (i = 0; i < rb->to_free; i++) {
struct io_kiocb *req = rb->reqs[i];
- if (req->flags & REQ_F_FIXED_FILE)
+ if (req->flags & REQ_F_FIXED_FILE) {
req->file = NULL;
+ fixed_refs++;
+ }
if (req->flags & REQ_F_INFLIGHT)
inflight++;
else
@@ -1255,8 +1259,9 @@ static void io_free_req_many(struct io_ring_ctx *ctx, struct req_batch *rb)
}
do_free:
kmem_cache_free_bulk(req_cachep, rb->to_free, rb->reqs);
+ if (fixed_refs)
+ percpu_ref_put_many(&ctx->file_data->refs, fixed_refs);
percpu_ref_put_many(&ctx->refs, rb->to_free);
- percpu_ref_put_many(&ctx->file_data->refs, rb->to_free);
rb->to_free = rb->need_iter = 0;
}
--
Jens Axboe
