From: Nadav Amit <namit@xxxxxxxxxx>
[ Upstream commit 20c0b380f971e7d48f5d978bc27d827f7eabb21a ]
The compiler should be forbidden from any strange optimization for async
writes to user visible data-structures. Without proper protection, the
compiler can cause write-tearing or invent writes that would confuse the
userspace.
However, there are writes to sq_flags which are not protected by
WRITE_ONCE(). Use WRITE_ONCE() for these writes.
This is purely a theoretical issue. Presumably, any compiler is very
unlikely to do such optimizations.
Fixes: 75b28affdd6a ("io_uring: allocate the two rings together")
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Pavel Begunkov <asml.silence@xxxxxxxxx>
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210808001342.964634-3-namit@xxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/io_uring.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index f23ff39f7697..0a5f105c657c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1482,7 +1482,8 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
if (all_flushed) {
clear_bit(0, &ctx->sq_check_overflow);
clear_bit(0, &ctx->cq_check_overflow);
- ctx->rings->sq_flags &= ~IORING_SQ_CQ_OVERFLOW;
+ WRITE_ONCE(ctx->rings->sq_flags,
+ ctx->rings->sq_flags & ~IORING_SQ_CQ_OVERFLOW);
}
if (posted)
@@ -1562,7 +1563,9 @@ static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data,
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;
+ WRITE_ONCE(ctx->rings->sq_flags,
+ ctx->rings->sq_flags | IORING_SQ_CQ_OVERFLOW);
+
}
ocqe->cqe.user_data = user_data;
ocqe->cqe.res = res;
@@ -6790,14 +6793,16 @@ static inline void io_ring_set_wakeup_flag(struct io_ring_ctx *ctx)
{
/* Tell userspace we may need a wakeup call */
spin_lock_irq(&ctx->completion_lock);
- ctx->rings->sq_flags |= IORING_SQ_NEED_WAKEUP;
+ WRITE_ONCE(ctx->rings->sq_flags,
+ ctx->rings->sq_flags | IORING_SQ_NEED_WAKEUP);
spin_unlock_irq(&ctx->completion_lock);
}
static inline void io_ring_clear_wakeup_flag(struct io_ring_ctx *ctx)
{
spin_lock_irq(&ctx->completion_lock);
- ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
+ WRITE_ONCE(ctx->rings->sq_flags,
+ ctx->rings->sq_flags & ~IORING_SQ_NEED_WAKEUP);
spin_unlock_irq(&ctx->completion_lock);
}
--
2.30.2
