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authorXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>2020-06-11 23:39:36 +0800
committerJens Axboe <axboe@kernel.dk>2020-06-11 09:45:21 -0600
commit65a6543da386838f935d2f03f452c5c0acff2a68 (patch)
tree21668dd9a1bb03b01ebc38eeb54367a8bcb4d485 /fs
parente697deed834de15d2322d0619d51893022c90ea2 (diff)
io_uring: fix io_kiocb.flags modification race in IOPOLL mode
While testing io_uring in arm, we found sometimes io_sq_thread() keeps polling io requests even though there are not inflight io requests in block layer. After some investigations, found a possible race about io_kiocb.flags, see below race codes: 1) in the end of io_write() or io_read() req->flags &= ~REQ_F_NEED_CLEANUP; kfree(iovec); return ret; 2) in io_complete_rw_iopoll() if (res != -EAGAIN) req->flags |= REQ_F_IOPOLL_COMPLETED; In IOPOLL mode, io requests still maybe completed by interrupt, then above codes are not safe, concurrent modifications to req->flags, which is not protected by lock or is not atomic modifications. I also had disassemble io_complete_rw_iopoll() in arm: req->flags |= REQ_F_IOPOLL_COMPLETED; 0xffff000008387b18 <+76>: ldr w0, [x19,#104] 0xffff000008387b1c <+80>: orr w0, w0, #0x1000 0xffff000008387b20 <+84>: str w0, [x19,#104] Seems that the "req->flags |= REQ_F_IOPOLL_COMPLETED;" is load and modification, two instructions, which obviously is not atomic. To fix this issue, add a new iopoll_completed in io_kiocb to indicate whether io request is completed. Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'fs')
-rw-r--r--fs/io_uring.c12
1 files changed, 6 insertions, 6 deletions
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5b0249140ff5..61fca5afaac8 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -529,7 +529,6 @@ enum {
REQ_F_INFLIGHT_BIT,
REQ_F_CUR_POS_BIT,
REQ_F_NOWAIT_BIT,
- REQ_F_IOPOLL_COMPLETED_BIT,
REQ_F_LINK_TIMEOUT_BIT,
REQ_F_TIMEOUT_BIT,
REQ_F_ISREG_BIT,
@@ -574,8 +573,6 @@ enum {
REQ_F_CUR_POS = BIT(REQ_F_CUR_POS_BIT),
/* must not punt to workers */
REQ_F_NOWAIT = BIT(REQ_F_NOWAIT_BIT),
- /* polled IO has completed */
- REQ_F_IOPOLL_COMPLETED = BIT(REQ_F_IOPOLL_COMPLETED_BIT),
/* has linked timeout */
REQ_F_LINK_TIMEOUT = BIT(REQ_F_LINK_TIMEOUT_BIT),
/* timeout request */
@@ -640,6 +637,8 @@ struct io_kiocb {
struct io_async_ctx *io;
int cflags;
u8 opcode;
+ /* polled IO has completed */
+ u8 iopoll_completed;
u16 buf_index;
@@ -1798,7 +1797,7 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
* If we find a request that requires polling, break out
* and complete those lists first, if we have entries there.
*/
- if (req->flags & REQ_F_IOPOLL_COMPLETED) {
+ if (READ_ONCE(req->iopoll_completed)) {
list_move_tail(&req->list, &done);
continue;
}
@@ -1979,7 +1978,7 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
req_set_fail_links(req);
req->result = res;
if (res != -EAGAIN)
- req->flags |= REQ_F_IOPOLL_COMPLETED;
+ WRITE_ONCE(req->iopoll_completed, 1);
}
/*
@@ -2012,7 +2011,7 @@ static void io_iopoll_req_issued(struct io_kiocb *req)
* For fast devices, IO may have already completed. If it has, add
* it to the front so we find it first.
*/
- if (req->flags & REQ_F_IOPOLL_COMPLETED)
+ if (READ_ONCE(req->iopoll_completed))
list_add(&req->list, &ctx->poll_list);
else
list_add_tail(&req->list, &ctx->poll_list);
@@ -2140,6 +2139,7 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
kiocb->ki_flags |= IOCB_HIPRI;
kiocb->ki_complete = io_complete_rw_iopoll;
req->result = 0;
+ req->iopoll_completed = 0;
} else {
if (kiocb->ki_flags & IOCB_HIPRI)
return -EINVAL;