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FAILED: patch "[PATCH] io_uring: Use WRITE_ONCE() when writing to sq_flags" failed to apply to 5.10-stable tree

PATCH [email protected] 1 participant 1 message Aug 16, 2021

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The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 20c0b380f971e7d48f5d978bc27d827f7eabb21a Mon Sep 17 00:00:00 2001
From: Nadav Amit <[email protected]>
Date: Sat, 7 Aug 2021 17:13:42 -0700
Subject: [PATCH] io_uring: Use WRITE_ONCE() when writing to sq_flags

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 <[email protected]>
Cc Pavel Begunkov <[email protected]>
Signed-off-by Nadav Amit <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Signed-off-by Jens Axboe <[email protected]>
fs/io_uring.c +9 -4
index 1093df3977b8..ca064486cb41 100644
@@ -1500,7 +1500,8 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
 	all_flushed = list_empty(&ctx->cq_overflow_list);
 	if (all_flushed) {
 		clear_bit(0, &ctx->check_cq_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)

@@ -1579,7 +1580,9 @@ 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->check_cq_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;

@@ -6804,14 +6807,16 @@ 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);
 }