linux-kernel - [PATCH] CXL: Fix afu_read() not doing finish

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Message-Id: <1412764803-sup-6790@delenn.ozlabs.ibm.com>
Date:	Wed, 08 Oct 2014 21:41:20 +1100
From:	Ian Munsie <imunsie@....ibm.com>
To:	greg <greg@...ah.com>, arnd <arnd@...db.de>,
	mpe <mpe@...erman.id.au>, benh <benh@...nel.crashing.org>
Cc:	mikey <mikey@...ling.org>, anton <anton@...ba.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linuxppc-dev <linuxppc-dev@...abs.org>, jk <jk@...abs.org>,
	imunsie <imunsie@....ibm.com>,
	cbe-oss-dev <cbe-oss-dev@...ts.ozlabs.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: [PATCH] CXL: Fix afu_read() not doing finish_wait() on signal or non-blocking

If afu_read() returned due to a signal or the AFU file descriptor being
opened non-blocking it would not call finish_wait() before returning,
which could lead to a crash later when something else wakes up the wait
queue.

This patch restructures the wait logic to ensure that the cleanup is
done correctly.

Signed-off-by: Ian Munsie <imunsie@....ibm.com>
---
 drivers/misc/cxl/file.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/misc/cxl/file.c b/drivers/misc/cxl/file.c
index 847b7e6..378b099 100644
--- a/drivers/misc/cxl/file.c
+++ b/drivers/misc/cxl/file.c
@@ -273,6 +273,7 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count,
        struct cxl_context *ctx = file->private_data;
        struct cxl_event event;
        unsigned long flags;
+       int rc;
        DEFINE_WAIT(wait);
 
        if (count < CXL_READ_MIN_SIZE)
@@ -285,13 +286,17 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count,
                if (ctx_event_pending(ctx))
                        break;
 
-               spin_unlock_irqrestore(&ctx->lock, flags);
-               if (file->f_flags & O_NONBLOCK)
-                       return -EAGAIN;
+               if (file->f_flags & O_NONBLOCK) {
+                       rc = -EAGAIN;
+                       goto out;
+               }
 
-               if (signal_pending(current))
-                       return -ERESTARTSYS;
+               if (signal_pending(current)) {
+                       rc = -ERESTARTSYS;
+                       goto out;
+               }
 
+               spin_unlock_irqrestore(&ctx->lock, flags);
                pr_devel("afu_read going to sleep...\n");
                schedule();
                pr_devel("afu_read woken up\n");
@@ -336,6 +341,11 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count,
        if (copy_to_user(buf, &event, event.header.size))
                return -EFAULT;
        return event.header.size;
+
+out:
+       finish_wait(&ctx->wq, &wait);
+       spin_unlock_irqrestore(&ctx->lock, flags);
+       return rc;
 }
 
 static const struct file_operations afu_fops = {
-- 
2.1.0

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