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author | Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com> | 2020-07-09 04:15:29 +0300 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2020-07-09 04:17:06 +0300 |
commit | 6d5f904904608a9cd32854d7d0a4dd65b27f9935 (patch) | |
tree | 2d862b5112e2cd9aae79a988e8c1a00768a5f122 | |
parent | b7db41c9e03b5189bc94993bd50e4506ac9e34c1 (diff) | |
download | linux-6d5f904904608a9cd32854d7d0a4dd65b27f9935.tar.xz |
io_uring: export cq overflow status to userspace
For those applications which are not willing to use io_uring_enter()
to reap and handle cqes, they may completely rely on liburing's
io_uring_peek_cqe(), but if cq ring has overflowed, currently because
io_uring_peek_cqe() is not aware of this overflow, it won't enter
kernel to flush cqes, below test program can reveal this bug:
static void test_cq_overflow(struct io_uring *ring)
{
struct io_uring_cqe *cqe;
struct io_uring_sqe *sqe;
int issued = 0;
int ret = 0;
do {
sqe = io_uring_get_sqe(ring);
if (!sqe) {
fprintf(stderr, "get sqe failed\n");
break;;
}
ret = io_uring_submit(ring);
if (ret <= 0) {
if (ret != -EBUSY)
fprintf(stderr, "sqe submit failed: %d\n", ret);
break;
}
issued++;
} while (ret > 0);
assert(ret == -EBUSY);
printf("issued requests: %d\n", issued);
while (issued) {
ret = io_uring_peek_cqe(ring, &cqe);
if (ret) {
if (ret != -EAGAIN) {
fprintf(stderr, "peek completion failed: %s\n",
strerror(ret));
break;
}
printf("left requets: %d\n", issued);
continue;
}
io_uring_cqe_seen(ring, cqe);
issued--;
printf("left requets: %d\n", issued);
}
}
int main(int argc, char *argv[])
{
int ret;
struct io_uring ring;
ret = io_uring_queue_init(16, &ring, 0);
if (ret) {
fprintf(stderr, "ring setup failed: %d\n", ret);
return 1;
}
test_cq_overflow(&ring);
return 0;
}
To fix this issue, export cq overflow status to userspace by adding new
IORING_SQ_CQ_OVERFLOW flag, then helper functions() in liburing, such as
io_uring_peek_cqe, can be aware of this cq overflow and do flush accordingly.
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r-- | fs/io_uring.c | 11 | ||||
-rw-r--r-- | include/uapi/linux/io_uring.h | 1 |
2 files changed, 10 insertions, 2 deletions
diff --git a/fs/io_uring.c b/fs/io_uring.c index d37d7ea5ebe5..32e37c38f274 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -1274,6 +1274,7 @@ static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force) if (cqe) { clear_bit(0, &ctx->sq_check_overflow); clear_bit(0, &ctx->cq_check_overflow); + ctx->rings->sq_flags &= ~IORING_SQ_CQ_OVERFLOW; } spin_unlock_irqrestore(&ctx->completion_lock, flags); io_cqring_ev_posted(ctx); @@ -1311,6 +1312,7 @@ static void __io_cqring_fill_event(struct io_kiocb *req, long res, long cflags) if (list_empty(&ctx->cq_overflow_list)) { set_bit(0, &ctx->sq_check_overflow); set_bit(0, &ctx->cq_check_overflow); + ctx->rings->sq_flags |= IORING_SQ_CQ_OVERFLOW; } req->flags |= REQ_F_OVERFLOW; refcount_inc(&req->refs); @@ -6080,9 +6082,9 @@ static int io_sq_thread(void *data) } /* Tell userspace we may need a wakeup call */ + spin_lock_irq(&ctx->completion_lock); ctx->rings->sq_flags |= IORING_SQ_NEED_WAKEUP; - /* make sure to read SQ tail after writing flags */ - smp_mb(); + spin_unlock_irq(&ctx->completion_lock); to_submit = io_sqring_entries(ctx); if (!to_submit || ret == -EBUSY) { @@ -6100,13 +6102,17 @@ static int io_sq_thread(void *data) schedule(); finish_wait(&ctx->sqo_wait, &wait); + spin_lock_irq(&ctx->completion_lock); ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP; + spin_unlock_irq(&ctx->completion_lock); ret = 0; continue; } finish_wait(&ctx->sqo_wait, &wait); + spin_lock_irq(&ctx->completion_lock); ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP; + spin_unlock_irq(&ctx->completion_lock); } mutex_lock(&ctx->uring_lock); @@ -7488,6 +7494,7 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx, if (list_empty(&ctx->cq_overflow_list)) { clear_bit(0, &ctx->sq_check_overflow); clear_bit(0, &ctx->cq_check_overflow); + ctx->rings->sq_flags &= ~IORING_SQ_CQ_OVERFLOW; } spin_unlock_irq(&ctx->completion_lock); diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h index 92c22699a5a7..7843742b8b74 100644 --- a/include/uapi/linux/io_uring.h +++ b/include/uapi/linux/io_uring.h @@ -197,6 +197,7 @@ struct io_sqring_offsets { * sq_ring->flags */ #define IORING_SQ_NEED_WAKEUP (1U << 0) /* needs io_uring_enter wakeup */ +#define IORING_SQ_CQ_OVERFLOW (1U << 1) /* CQ ring is overflown */ struct io_cqring_offsets { __u32 head; |