+ dax-busc-use-the-right-locking-mode-read-vs-write-in-size_show.patch added to mm-unstable branch

+ dax-busc-use-the-right-locking-mode-read-vs-write-in-size_show.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: dax/bus.c: use the right locking mode (read vs write) in size_show
has been added to the -mm mm-unstable branch.  Its filename is
     dax-busc-use-the-right-locking-mode-read-vs-write-in-size_show.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/dax-busc-use-the-right-locking-mode-read-vs-write-in-size_show.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Vishal Verma <vishal.l.verma@intel.com>
Subject: dax/bus.c: use the right locking mode (read vs write) in size_show
Date: Tue, 30 Apr 2024 11:44:26 -0600

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.

Link: https://lkml.kernel.org/r/20240430-vv-dax_abi_fixes-v3-4-e3dcd755774c@intel.com
Fixes: c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local rwsem")
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/dax/bus.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/dax/bus.c~dax-busc-use-the-right-locking-mode-read-vs-write-in-size_show
+++ a/drivers/dax/bus.c
@@ -937,11 +937,11 @@ static ssize_t size_show(struct device *
 	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);
 }
_

Patches currently in -mm which might be from vishal.l.verma@intel.com are

dax-busc-replace-warn_on_once-with-lockdep-asserts.patch
dax-busc-fix-locking-for-unregister_dax_dev-unregister_dax_mapping-paths.patch
dax-busc-dont-use-down_write_killable-for-non-user-processes.patch
dax-busc-use-the-right-locking-mode-read-vs-write-in-size_show.patch