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Message-ID: <tencent_DC522F05F54C72A6EF3193F9313CD756350A@qq.com>
Date: Thu, 13 Jul 2023 00:42:32 +0800
From: wenyang.linux@...mail.com
To: Alexander Viro <viro@...iv.linux.org.uk>,
Jens Axboe <axboe@...nel.dk>,
Christian Brauner <brauner@...nel.org>
Cc: Wen Yang <wenyang.linux@...mail.com>,
Christoph Hellwig <hch@....de>, Dylan Yudaken <dylany@...com>,
David Woodhouse <dwmw@...zon.co.uk>,
Matthew Wilcox <willy@...radead.org>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] eventfd: avoid unnecessary wakeups in eventfd_write()
From: Wen Yang <wenyang.linux@...mail.com>
In eventfd_write(), when ucnt is 0 and ctx->count is also 0,
current->in_eventfd will be set to 1, which may affect eventfd_signal(),
and unnecessary wakeups will also be performed.
Fix this issue by ensuring that ctx->count is not zero.
Signed-off-by: Wen Yang <wenyang.linux@...mail.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Christian Brauner <brauner@...nel.org>
Cc: Christoph Hellwig <hch@....de>
Cc: Dylan Yudaken <dylany@...com>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
fs/eventfd.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/eventfd.c b/fs/eventfd.c
index 33a918f9566c..254b18ff0e00 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -281,10 +281,12 @@ static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t c
}
if (likely(res > 0)) {
ctx->count += ucnt;
- current->in_eventfd = 1;
- if (waitqueue_active(&ctx->wqh))
- wake_up_locked_poll(&ctx->wqh, EPOLLIN);
- current->in_eventfd = 0;
+ if (ctx->count) {
+ current->in_eventfd = 1;
+ if (waitqueue_active(&ctx->wqh))
+ wake_up_locked_poll(&ctx->wqh, EPOLLIN);
+ current->in_eventfd = 0;
+ }
}
spin_unlock_irq(&ctx->wqh.lock);
--
2.25.1
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