lkml.org 
[lkml]   [2021]   [Aug]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 5.13 002/127] io_uring: Use WRITE_ONCE() when writing to sq_flags
Date
From: Nadav Amit <namit@vmware.com>

[ 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@kernel.dk>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Nadav Amit <namit@vmware.com>
Link: https://lore.kernel.org/r/20210808001342.964634-3-namit@vmware.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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
\
 
 \ /
  Last update: 2021-08-24 18:57    [W:0.318 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site