The patch titled
Subject: dax/bus.c: fix locking for unregister_dax_dev / unregister_dax_mapping paths
has been added to the -mm mm-unstable branch. Its filename is
dax-busc-fix-locking-for-unregister_dax_dev-unregister_dax_mapping-paths.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/dax-busc-fix-locking-for-unregister_dax_dev-unregister_dax_mapping-paths.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@xxxxxxxxx>
Subject: dax/bus.c: fix locking for unregister_dax_dev / unregister_dax_mapping paths
Date: Tue, 30 Apr 2024 11:44:24 -0600
Commit c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local
rwsem") aimed to undo device_lock() abuses for protecting changes to
dax-driver internal data-structures like the dax_region resource tree to
device-dax-instance range structures. However, the device_lock() was
legitimately enforcing that devices to be deleted were not current
actively attached to any driver nor assigned any capacity from the region.
As a result of the device_lock restoration in delete_store(), the
conditional locking in unregister_dev_dax() and unregister_dax_mapping()
can be removed.
Link: https://lkml.kernel.org/r/20240430-vv-dax_abi_fixes-v3-2-e3dcd755774c@xxxxxxxxx
Fixes: c05ae9d85b47 ("dax/bus.c: replace driver-core lock usage by a local rwsem")
Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Alison Schofield <alison.schofield@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/dax/bus.c | 42 ++++++++----------------------------------
1 file changed, 8 insertions(+), 34 deletions(-)
--- a/drivers/dax/bus.c~dax-busc-fix-locking-for-unregister_dax_dev-unregister_dax_mapping-paths
+++ a/drivers/dax/bus.c
@@ -465,26 +465,17 @@ static void free_dev_dax_ranges(struct d
trim_dev_dax_range(dev_dax);
}
-static void __unregister_dev_dax(void *dev)
+static void unregister_dev_dax(void *dev)
{
struct dev_dax *dev_dax = to_dev_dax(dev);
dev_dbg(dev, "%s\n", __func__);
+ down_write(&dax_region_rwsem);
kill_dev_dax(dev_dax);
device_del(dev);
free_dev_dax_ranges(dev_dax);
put_device(dev);
-}
-
-static void unregister_dev_dax(void *dev)
-{
- if (rwsem_is_locked(&dax_region_rwsem))
- return __unregister_dev_dax(dev);
-
- if (WARN_ON_ONCE(down_write_killable(&dax_region_rwsem) != 0))
- return;
- __unregister_dev_dax(dev);
up_write(&dax_region_rwsem);
}
@@ -560,15 +551,10 @@ static ssize_t delete_store(struct devic
if (!victim)
return -ENXIO;
- rc = down_write_killable(&dax_region_rwsem);
- if (rc)
- return rc;
- rc = down_write_killable(&dax_dev_rwsem);
- if (rc) {
- up_write(&dax_region_rwsem);
- return rc;
- }
+ device_lock(dev);
+ device_lock(victim);
dev_dax = to_dev_dax(victim);
+ down_write(&dax_dev_rwsem);
if (victim->driver || dev_dax_size(dev_dax))
rc = -EBUSY;
else {
@@ -589,11 +575,12 @@ static ssize_t delete_store(struct devic
rc = -EBUSY;
}
up_write(&dax_dev_rwsem);
+ device_unlock(victim);
/* won the race to invalidate the device, clean it up */
if (do_del)
devm_release_action(dev, unregister_dev_dax, victim);
- up_write(&dax_region_rwsem);
+ device_unlock(dev);
put_device(victim);
return rc;
@@ -705,7 +692,7 @@ static void dax_mapping_release(struct d
put_device(parent);
}
-static void __unregister_dax_mapping(void *data)
+static void unregister_dax_mapping(void *data)
{
struct device *dev = data;
struct dax_mapping *mapping = to_dax_mapping(dev);
@@ -713,25 +700,12 @@ static void __unregister_dax_mapping(voi
dev_dbg(dev, "%s\n", __func__);
- lockdep_assert_held_write(&dax_region_rwsem);
-
dev_dax->ranges[mapping->range_id].mapping = NULL;
mapping->range_id = -1;
device_unregister(dev);
}
-static void unregister_dax_mapping(void *data)
-{
- if (rwsem_is_locked(&dax_region_rwsem))
- return __unregister_dax_mapping(data);
-
- if (WARN_ON_ONCE(down_write_killable(&dax_region_rwsem) != 0))
- return;
- __unregister_dax_mapping(data);
- up_write(&dax_region_rwsem);
-}
-
static struct dev_dax_range *get_dax_range(struct device *dev)
{
struct dax_mapping *mapping = to_dax_mapping(dev);
_
Patches currently in -mm which might be from vishal.l.verma@xxxxxxxxx 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
