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SubjectRe: [PATCH] rcu_read_lock/unlock protect find_task_by_vpid call
On Sun, Oct 31, 2010 at 08:33:35AM +0900, Tetsuo Handa wrote:
> Paul E. McKenney wrote:
> > So we should remove the lockdep_tasklist_lock_is_held() and then
> > apply Sergey's patch, correct?
>
> Yes. rcu_lockdep_assert(rcu_read_lock_held()) in find_task_by_pid_ns()
> is correct and callers need to use rcu_read_lock().
>
> As of 2.6.32, there are 20+ users who missed rcu_read_lock().
> So, similar reports will be posted like popcorn.
> http://kerneltrap.org/mailarchive/linux-kernel/2009/12/11/4518016

OK, let's see how these are in 2.6.36... The summary is that almost
all of the popcorn kernels have already popped.

> Users missing read_lock(&tasklist_lock) when calling find_task_by_vpid():
>
> get_net_ns_by_pid() in net/core/net_namespace.c

Fixed with rcu_read_lock().

> seq_print_userip_objs() in kernel/trace/trace_output.c

Fixed with rcu_read_lock().

> fill_pid() in kernel/taskstats.c

This one seems to be named fill_stats_for_pid(), and it
is fixed with rcu_read_lock().

> fill_tgid() in kernel/taskstats.c

This one seems to be named fill_stats_for_tgid(), and it
is fixed with rcu_read_lock().

> futex_find_get_task() in kernel/futex.c

Fixed with rcu_read_lock().

> SYSCALL_DEFINE3(get_robust_list) in kernel/futex.c

Fixed with rcu_read_lock().

> compat_sys_get_robust_list() in kernel/futex_compat.c

Fixed with rcu_read_lock().

> ptrace_get_task_struct() in kernel/ptrace.c

Fixed with rcu_read_lock().

> do_send_specific() in kernel/signal.c

Fixed with rcu_read_lock().

> find_get_context() in kernel/perf_event.c

Fixed with rcu_read_lock() plus code motion.

> posix_cpu_clock_get() in kernel/posix-cpu-timers.c

Fixed with rcu_read_lock().

> good_sigevent() in kernel/posix-timers.c

Fixed with rcu_read_lock() in caller.

> attach_task_by_pid() in kernel/cgroup.c

Fixed with rcu_read_lock().

> SYSCALL_DEFINE1(getpgid) in kernel/sys.c

Fixed with rcu_read_lock().

> SYSCALL_DEFINE1(getsid) in kernel/sys.c

Fixed with rcu_read_lock().

> do_sched_setscheduler() in kernel/sched.c

Fixed with rcu_read_lock().

>
> Users missing rcu_read_lock() when calling find_task_by_vpid():
>
> SYSCALL_DEFINE3(ioprio_set) in fs/ioprio.c

Patches in flight.

> SYSCALL_DEFINE2(ioprio_get) in fs/ioprio.c

Patches in flight.

> cap_get_target_pid() in kernel/capability.c

Fixed with rcu_read_lock().

> audit_prepare_user_tty() in kernel/audit.c

Fixed with rcu_read_lock().

> audit_receive_msg() in kernel/audit.c

Fixed with rcu_read_lock(), two instances.

> check_clock() in kernel/posix-cpu-timers.c

This one has read_lock(&tasklist_lock).

> posix_cpu_timer_create() in kernel/posix-cpu-timers.c

This one has read_lock(&tasklist_lock).

> SYSCALL_DEFINE3(setpriority) in kernel/sys.c

This one has both read_lock(&tasklist_lock) and rcu_read_lock().
Both belt -and- suspenders...

> SYSCALL_DEFINE2(getpriority) in kernel/sys.c

Ditto.

> SYSCALL_DEFINE2(setpgid) in kernel/sys.c

This one has both write_lock_irq(&tasklist_lock) and
rcu_read_lock(). -Serious- belt along with the suspenders...

> SYSCALL_DEFINE1(sched_getscheduler) in kernel/sched.c

Fixed with rcu_read_lock().

> SYSCALL_DEFINE2(sched_getparam) in kernel/sched.c

Fixed with rcu_read_lock().

> sched_setaffinity() in kernel/sched.c

Fixed with rcu_read_lock().

> sched_getaffinity() in kernel/sched.c

Fixed with rcu_read_lock().

> SYSCALL_DEFINE2(sched_rr_get_interval) in kernel/sched.c

Fixed with rcu_read_lock().

> tomoyo_is_select_one() in security/tomoyo/common.c

This one has both read_lock(&tasklist_lock) and rcu_read_lock().
Both belt -and- suspenders... (Also renamed to tomoyo_select_one().)

> tomoyo_read_pid() in security/tomoyo/common.c

This one has both read_lock(&tasklist_lock) and rcu_read_lock().
Both belt -and- suspenders...

> SYSCALL_DEFINE6(move_pages) in mm/migrate.c

This one does read_lock(&tasklist_lock).

> SYSCALL_DEFINE4(migrate_pages) in mm/mempolicy.c

No call to find_task_by_vpid() in migrate_pages() anymore,
but there is one protected by read_lock(&tasklist_lock) in
move_pages().

> find_process_by_pid() in arch/mips/kernel/mips-mt-fpaff.c

No change, so let's check the callers:

mipsmt_sys_sched_setaffinity(): rcu_read_lock().
mipsmt_sys_sched_getaffinity(): read_lock(&tasklist_lock).
do_sched_setscheduler(): rcu_read_lock().
sched_getscheduler(): rcu_read_lock().
sched_getparam(): rcu_read_lock().
sched_setaffinity(): rcu_read_lock().
sched_getaffinity(); rcu_read_lock().
sched_rr_get_interval(): rcu_read_lock().

So all of these are protected.

> pfm_get_task() in arch/ia64/kernel/perfmon.c

This one does read_lock(&tasklist_lock).

> cxn_pin_by_pid() in arch/frv/mm/mmu-context.c

This one does read_lock(&tasklist_lock).

>
> Users missing read_lock(&tasklist_lock) when calling find_task_by_pid_ns():
>
> rest_init() in init/main.c

Fixed with rcu_read_lock().

> proc_pid_lookup() in fs/proc/base.c

Fixed with rcu_read_lock().

> proc_task_lookup() in fs/proc/base.c

Fixed with rcu_read_lock().

> first_tid() in fs/proc/base.c

Fixed with rcu_read_lock().

> getthread() in kernel/kgdb.c

This is now in kernel/debug/gdbstub.c... It looks to need
an rcu_read_lock(). It has a comment, but...

> mconsole_stack() in arch/um/drivers/mconsole_kern.c

This one still needs help.

>
> Users missing rcu_read_lock() when calling find_task_by_pid_ns():
>
> rest_init() in init/main.c

Fixed with rcu_read_lock().

> getthread() in kernel/kgdb.c

This one still needs help.

> mconsole_stack() in arch/um/drivers/mconsole_kern.c

This one still needs help.

So mostly there...

Thanx, Paul


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