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zvol: remove the OS-side minor before freeing the zvol

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When destroying a zvol, it is not "unpublished" from the system (that
is, /dev/zd* node removed) until zvol_os_free(). Under Linux, at the
time del_gendisk() and put_disk() are called, the device node may still
be have an active hold, from a userspace program or something inside the
kernel (a partition probe). As it is currently, this can lead to calls
to zvol_open() or zvol_release() while the zvol_state_t is partially or
fully freed. zvol_open() has some protection against this by checking
that private_data is NULL, but zvol_release does not.

This implements a better ordering for all of this by adding a new
OS-side method, zvol_os_remove_minor(), which is responsible for fully
decoupling the "private" (OS-side) objects from the zvol_state_t. For
Linux, that means calling put_disk(), nulling private_data, and freeing
zv_zso.

This takes the place of zvol_os_clear_private(), which was a nod in that
direction but did not do enough, and did not do it early enough.

Equivalent changes are made on the FreeBSD side to follow the API
change.

Sponsored-by: Klara, Inc.
Sponsored-by: Railway Corporation
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Fedor Uporov <fuporov.vstack@gmail.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17625
This commit is contained in:
Rob Norris
2025-08-05 13:43:17 +10:00
committed by Brian Behlendorf
parent b2c792778c
commit 96f9d271ea
4 changed files with 99 additions and 96 deletions
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module/zfs/zvol.c
+4 -9
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@@ -38,7 +38,7 @@
* Copyright 2014 Nexenta Systems, Inc. All rights reserved.
* Copyright (c) 2016 Actifio, Inc. All rights reserved.
* Copyright (c) 2012, 2019 by Delphix. All rights reserved.
* Copyright (c) 2024, Klara, Inc.
* Copyright (c) 2024, 2025, Klara, Inc.
*/
/*
@@ -1599,8 +1599,8 @@ zvol_remove_minor_task(void *arg)
rw_enter(&zvol_state_lock, RW_WRITER);
mutex_enter(&zv->zv_state_lock);
zvol_os_remove_minor(zv);
zvol_remove(zv);
zvol_os_clear_private(zv);
mutex_exit(&zv->zv_state_lock);
rw_exit(&zvol_state_lock);
@@ -1669,9 +1669,9 @@ zvol_remove_minors_impl(zvol_task_t *task)
* If in use, try to throw everyone off and try again
* later.
*/
zv->zv_flags |= ZVOL_REMOVING;
if (zv->zv_open_count > 0 ||
atomic_read(&zv->zv_suspend_ref)) {
zv->zv_flags |= ZVOL_REMOVING;
t = taskq_dispatch(
zv->zv_objset->os_spa->spa_zvol_taskq,
zvol_remove_minor_task, zv, TQ_SLEEP);
@@ -1687,14 +1687,9 @@ zvol_remove_minors_impl(zvol_task_t *task)
continue;
}
zvol_os_remove_minor(zv);
zvol_remove(zv);
/*
* Cleared while holding zvol_state_lock as a writer
* which will prevent zvol_open() from opening it.
*/
zvol_os_clear_private(zv);
/* Drop zv_state_lock before zvol_free() */
mutex_exit(&zv->zv_state_lock);