linux/block/ioprio.c
Jan Kara 4b838d9ee9 block: Fix handling of tasks without ioprio in ioprio_get(2)
ioprio_get(2) can be asked to return the best IO priority from several
tasks (IOPRIO_WHO_PGRP, IOPRIO_WHO_USER). Currently the call treats
tasks without set IO priority as having priority
IOPRIO_CLASS_BE/IOPRIO_BE_NORM however this does not really reflect the
IO priority the task will get (which depends on task's nice value).

Fix the code to use the real IO priority task's IO will use. We have to
modify code for ioprio_get(IOPRIO_WHO_PROCESS) to keep returning
IOPRIO_CLASS_NONE priority for tasks without set IO priority as a
special case to maintain userspace visible API.

Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Tested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220623074840.5960-5-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2022-06-27 06:29:12 -06:00

279 lines
5.8 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* fs/ioprio.c
*
* Copyright (C) 2004 Jens Axboe <axboe@kernel.dk>
*
* Helper functions for setting/querying io priorities of processes. The
* system calls closely mimmick getpriority/setpriority, see the man page for
* those. The prio argument is a composite of prio class and prio data, where
* the data argument has meaning within that class. The standard scheduling
* classes have 8 distinct prio levels, with 0 being the highest prio and 7
* being the lowest.
*
* IOW, setting BE scheduling class with prio 2 is done ala:
*
* unsigned int prio = (IOPRIO_CLASS_BE << IOPRIO_CLASS_SHIFT) | 2;
*
* ioprio_set(PRIO_PROCESS, pid, prio);
*
* See also Documentation/block/ioprio.rst
*
*/
#include <linux/gfp.h>
#include <linux/kernel.h>
#include <linux/ioprio.h>
#include <linux/cred.h>
#include <linux/blkdev.h>
#include <linux/capability.h>
#include <linux/syscalls.h>
#include <linux/security.h>
#include <linux/pid_namespace.h>
int ioprio_check_cap(int ioprio)
{
int class = IOPRIO_PRIO_CLASS(ioprio);
int data = IOPRIO_PRIO_DATA(ioprio);
switch (class) {
case IOPRIO_CLASS_RT:
/*
* Originally this only checked for CAP_SYS_ADMIN,
* which was implicitly allowed for pid 0 by security
* modules such as SELinux. Make sure we check
* CAP_SYS_ADMIN first to avoid a denial/avc for
* possibly missing CAP_SYS_NICE permission.
*/
if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
return -EPERM;
fallthrough;
/* rt has prio field too */
case IOPRIO_CLASS_BE:
if (data >= IOPRIO_NR_LEVELS || data < 0)
return -EINVAL;
break;
case IOPRIO_CLASS_IDLE:
break;
case IOPRIO_CLASS_NONE:
if (data)
return -EINVAL;
break;
default:
return -EINVAL;
}
return 0;
}
SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
{
struct task_struct *p, *g;
struct user_struct *user;
struct pid *pgrp;
kuid_t uid;
int ret;
ret = ioprio_check_cap(ioprio);
if (ret)
return ret;
ret = -ESRCH;
rcu_read_lock();
switch (which) {
case IOPRIO_WHO_PROCESS:
if (!who)
p = current;
else
p = find_task_by_vpid(who);
if (p)
ret = set_task_ioprio(p, ioprio);
break;
case IOPRIO_WHO_PGRP:
if (!who)
pgrp = task_pgrp(current);
else
pgrp = find_vpid(who);
read_lock(&tasklist_lock);
do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
ret = set_task_ioprio(p, ioprio);
if (ret) {
read_unlock(&tasklist_lock);
goto out;
}
} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
read_unlock(&tasklist_lock);
break;
case IOPRIO_WHO_USER:
uid = make_kuid(current_user_ns(), who);
if (!uid_valid(uid))
break;
if (!who)
user = current_user();
else
user = find_user(uid);
if (!user)
break;
for_each_process_thread(g, p) {
if (!uid_eq(task_uid(p), uid) ||
!task_pid_vnr(p))
continue;
ret = set_task_ioprio(p, ioprio);
if (ret)
goto free_uid;
}
free_uid:
if (who)
free_uid(user);
break;
default:
ret = -EINVAL;
}
out:
rcu_read_unlock();
return ret;
}
/*
* If the task has set an I/O priority, use that. Otherwise, return
* the default I/O priority.
*
* Expected to be called for current task or with task_lock() held to keep
* io_context stable.
*/
int __get_task_ioprio(struct task_struct *p)
{
struct io_context *ioc = p->io_context;
int prio;
if (p != current)
lockdep_assert_held(&p->alloc_lock);
if (ioc)
prio = ioc->ioprio;
else
prio = IOPRIO_DEFAULT;
if (IOPRIO_PRIO_CLASS(prio) == IOPRIO_CLASS_NONE)
prio = IOPRIO_PRIO_VALUE(task_nice_ioclass(p),
task_nice_ioprio(p));
return prio;
}
EXPORT_SYMBOL_GPL(__get_task_ioprio);
static int get_task_ioprio(struct task_struct *p)
{
int ret;
ret = security_task_getioprio(p);
if (ret)
goto out;
task_lock(p);
ret = __get_task_ioprio(p);
task_unlock(p);
out:
return ret;
}
/*
* Return raw IO priority value as set by userspace. We use this for
* ioprio_get(pid, IOPRIO_WHO_PROCESS) so that we keep historical behavior and
* also so that userspace can distinguish unset IO priority (which just gets
* overriden based on task's nice value) from IO priority set to some value.
*/
static int get_task_raw_ioprio(struct task_struct *p)
{
int ret;
ret = security_task_getioprio(p);
if (ret)
goto out;
task_lock(p);
if (p->io_context)
ret = p->io_context->ioprio;
else
ret = IOPRIO_DEFAULT;
task_unlock(p);
out:
return ret;
}
static int ioprio_best(unsigned short aprio, unsigned short bprio)
{
return min(aprio, bprio);
}
SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
{
struct task_struct *g, *p;
struct user_struct *user;
struct pid *pgrp;
kuid_t uid;
int ret = -ESRCH;
int tmpio;
rcu_read_lock();
switch (which) {
case IOPRIO_WHO_PROCESS:
if (!who)
p = current;
else
p = find_task_by_vpid(who);
if (p)
ret = get_task_raw_ioprio(p);
break;
case IOPRIO_WHO_PGRP:
if (!who)
pgrp = task_pgrp(current);
else
pgrp = find_vpid(who);
read_lock(&tasklist_lock);
do_each_pid_thread(pgrp, PIDTYPE_PGID, p) {
tmpio = get_task_ioprio(p);
if (tmpio < 0)
continue;
if (ret == -ESRCH)
ret = tmpio;
else
ret = ioprio_best(ret, tmpio);
} while_each_pid_thread(pgrp, PIDTYPE_PGID, p);
read_unlock(&tasklist_lock);
break;
case IOPRIO_WHO_USER:
uid = make_kuid(current_user_ns(), who);
if (!who)
user = current_user();
else
user = find_user(uid);
if (!user)
break;
for_each_process_thread(g, p) {
if (!uid_eq(task_uid(p), user->uid) ||
!task_pid_vnr(p))
continue;
tmpio = get_task_ioprio(p);
if (tmpio < 0)
continue;
if (ret == -ESRCH)
ret = tmpio;
else
ret = ioprio_best(ret, tmpio);
}
if (who)
free_uid(user);
break;
default:
ret = -EINVAL;
}
rcu_read_unlock();
return ret;
}