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bcachefs: Fix sysfs warning in fstests generic/730,731

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sysfs warns if we're removing a symlink from a directory that's no
longer in sysfs; this is triggered by fstests generic/730, which
simulates hot removal of a block device.

This patch is however not a correct fix, since checking
kobj->state_in_sysfs on a kobj owned by another subsystem is racy.

A better fix would be to add the appropriate check to
sysfs_remove_link() - and sysfs_create_link() as well.

But kobject_add_internal()/kobject_del() do not as of today have locking
that would support that.

Note that the block/holder.c code appears to be subject to this race as
well.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc:  Christoph Hellwig <hch@lst.de>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2024-10-12 14:36:38 -04:00
parent cb6055e66f
commit 5e3b72324d
1 changed files with 24 additions and 10 deletions
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34
fs/bcachefs/super.c
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@ -184,6 +184,7 @@ static DEFINE_MUTEX(bch_fs_list_lock);
DECLARE_WAIT_QUEUE_HEAD(bch2_read_only_wait);
static void bch2_dev_unlink(struct bch_dev *);
static void bch2_dev_free(struct bch_dev *);
static int bch2_dev_alloc(struct bch_fs *, unsigned);
static int bch2_dev_sysfs_online(struct bch_fs *, struct bch_dev *);
@ -620,9 +621,7 @@ void __bch2_fs_stop(struct bch_fs *c)
up_write(&c->state_lock);
for_each_member_device(c, ca)
if (ca->kobj.state_in_sysfs &&
ca->disk_sb.bdev)
sysfs_remove_link(bdev_kobj(ca->disk_sb.bdev), "bcachefs");
bch2_dev_unlink(ca);
if (c->kobj.state_in_sysfs)
kobject_del(&c->kobj);
@ -1187,9 +1186,7 @@ static void bch2_dev_free(struct bch_dev *ca)
{
cancel_work_sync(&ca->io_error_work);
if (ca->kobj.state_in_sysfs &&
ca->disk_sb.bdev)
sysfs_remove_link(bdev_kobj(ca->disk_sb.bdev), "bcachefs");
bch2_dev_unlink(ca);
if (ca->kobj.state_in_sysfs)
kobject_del(&ca->kobj);
@ -1226,10 +1223,7 @@ static void __bch2_dev_offline(struct bch_fs *c, struct bch_dev *ca)
percpu_ref_kill(&ca->io_ref);
wait_for_completion(&ca->io_ref_completion);
if (ca->kobj.state_in_sysfs) {
sysfs_remove_link(bdev_kobj(ca->disk_sb.bdev), "bcachefs");
sysfs_remove_link(&ca->kobj, "block");
}
bch2_dev_unlink(ca);
bch2_free_super(&ca->disk_sb);
bch2_dev_journal_exit(ca);
@ -1251,6 +1245,26 @@ static void bch2_dev_io_ref_complete(struct percpu_ref *ref)
complete(&ca->io_ref_completion);
}
static void bch2_dev_unlink(struct bch_dev *ca)
{
struct kobject *b;
/*
* This is racy w.r.t. the underlying block device being hot-removed,
* which removes it from sysfs.
*
* It'd be lovely if we had a way to handle this race, but the sysfs
* code doesn't appear to provide a good method and block/holder.c is
* susceptible as well:
*/
if (ca->kobj.state_in_sysfs &&
ca->disk_sb.bdev &&
(b = bdev_kobj(ca->disk_sb.bdev))->state_in_sysfs) {
sysfs_remove_link(b, "bcachefs");
sysfs_remove_link(&ca->kobj, "block");
}
}
static int bch2_dev_sysfs_online(struct bch_fs *c, struct bch_dev *ca)
{
int ret;