From: Xiaoguang Wang <xiaoguang.w...@linux.alibaba.com>
[ Upstream commit 65a6543da386838f935d2f03f452c5c0acff2a68 ]
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.w...@linux.alibaba.com>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
fs/io_uring.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -513,7 +513,6 @@ 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,
@@ -556,8 +555,6 @@ 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 */
@@ -618,6 +615,8 @@ struct io_kiocb {
int cflags;
bool needs_fixed_file;
u8 opcode;
+ /* polled IO has completed */
+ u8 iopoll_completed;
u16 buf_index;
@@ -1760,7 +1759,7 @@ static int io_do_iopoll(struct io_ring_c
* 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;
}
@@ -1941,7 +1940,7 @@ static void io_complete_rw_iopoll(struct
req_set_fail_links(req);
req->result = res;
if (res != -EAGAIN)
- req->flags |= REQ_F_IOPOLL_COMPLETED;
+ WRITE_ONCE(req->iopoll_completed, 1);
}
/*
@@ -1974,7 +1973,7 @@ static void io_iopoll_req_issued(struct
* 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);
@@ -2098,6 +2097,7 @@ static int io_prep_rw(struct io_kiocb *r
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;
