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From: Vishal Verma <vishal.l.verma@intel.com>
Date: Tue, 30 Apr 2024 11:44:26 -0600
Subject: [PATCH v3 4/4] dax/bus.c: Use the right locking mode (read vs
 write) in size_show
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Message-Id: <20240430-vv-dax_abi_fixes-v3-4-e3dcd755774c@intel.com>
References: <20240430-vv-dax_abi_fixes-v3-0-e3dcd755774c@intel.com>
In-Reply-To: <20240430-vv-dax_abi_fixes-v3-0-e3dcd755774c@intel.com>
To: Dan Williams <dan.j.williams@intel.com>, 
 Dave Jiang <dave.jiang@intel.com>, 
 Alison Schofield <alison.schofield@intel.com>, 
 Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, 
 linux-kernel@vger.kernel.org, Vishal Verma <vishal.l.verma@intel.com>

In size_show(), the dax_dev_rwsem only needs a read lock, but was
acquiring a write lock. Change it to down_read_interruptible() so it
doesn't unnecessarily hold a write lock.

Fixes: c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local rwsem")
Cc: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 drivers/dax/bus.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 0011a6e6a8f2..f24b67c64d5e 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -937,11 +937,11 @@ static ssize_t size_show(struct device *dev,
 	unsigned long long size;
 	int rc;
 
-	rc = down_write_killable(&dax_dev_rwsem);
+	rc = down_read_interruptible(&dax_dev_rwsem);
 	if (rc)
 		return rc;
 	size = dev_dax_size(dev_dax);
-	up_write(&dax_dev_rwsem);
+	up_read(&dax_dev_rwsem);
 
 	return sysfs_emit(buf, "%llu\n", size);
 }

-- 
2.44.0