On (11/08/10 13:01), Davidlohr Bueso wrote:
> On Fri, 2010-10-29 at 15:55 +0300, Sergey Senozhatsky wrote:
> > Commit 4221a9918e38b7494cee341dda7b7b4bb8c04bde "Add RCU check for
> > find_task_by_vpid()" introduced rcu_lockdep_assert to find_task_by_pid_ns.
> > Assertion failed in sys_ioprio_get. The patch is fixing assertion
> > failure in ioprio_set as well.
> >
> > ===================================================
> > [ INFO: suspicious rcu_dereference_check() usage. ]
> > ---------------------------------------------------
> > kernel/pid.c:419 invoked rcu_dereference_check() without protection!
> >
> > rcu_scheduler_active = 1, debug_locks = 0
> > 1 lock held by iotop/4254:
> > #0: (tasklist_lock){.?.?..}, at: [<ffffffff811104b4>] sys_ioprio_get+0x22/0x2da
> >
> > stack backtrace:
> > Pid: 4254, comm: iotop Not tainted
> > Call Trace:
> > [<ffffffff810656f2>] lockdep_rcu_dereference+0xaa/0xb2
> > [<ffffffff81053c67>] find_task_by_pid_ns+0x4f/0x68
> > [<ffffffff81053c9d>] find_task_by_vpid+0x1d/0x1f
> > [<ffffffff811104e2>] sys_ioprio_get+0x50/0x2da
> > [<ffffffff81002182>] system_call_fastpath+0x16/0x1b
> >
> >
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> >
> > ---
> >
> > diff --git a/fs/ioprio.c b/fs/ioprio.c
> > index 748cfb9..666343d 100644
> > --- a/fs/ioprio.c
> > +++ b/fs/ioprio.c
> > @@ -113,8 +113,11 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
> > case IOPRIO_WHO_PROCESS:
> > if (!who)
> > p = current;
> > - else
> > + else {
> > + rcu_read_lock();
> > p = find_task_by_vpid(who);
> > + rcu_read_unlock();
> > + }
> > if (p)
> > ret = set_task_ioprio(p, ioprio);
> > break;
> > @@ -202,8 +205,11 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
> > case IOPRIO_WHO_PROCESS:
> > if (!who)
> > p = current;
> > - else
> > + else {
> > + rcu_read_lock();
> > p = find_task_by_vpid(who);
> > + rcu_read_unlock();
> > + }
> > if (p)
> > ret = get_task_ioprio(p);
> > break;
>
> If you add the rcu_read_lock/unlock() sections, we would also need to
> update the comment above accordingly.
>
Hello,
I think, this comment is relevant to IOPRIO_WHO_PGRP/IOPRIO_WHO_USER cases.
I only touched IOPRIO_WHO_PROCESS and IOPRIO_WHO_PROCESS.
So, imho, no need to remove it.
Sergey
>
> From: Davidlohr Bueso <dave@xxxxxxx>
> Subject: [PATCH] ioprio: remove comment to not use RCU
>
> Signed-off-by: Davidlohr Bueso <dave@xxxxxxx>
> ---
> fs/ioprio.c | 5 -----
> 1 files changed, 0 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ioprio.c b/fs/ioprio.c
> index 748cfb9..72d71de 100644
> --- a/fs/ioprio.c
> +++ b/fs/ioprio.c
> @@ -103,11 +103,6 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who,
> int, ioprio)
> }
>
> ret = -ESRCH;
> - /*
> - * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
> - * so we can't use rcu_read_lock(). See re-copy of ->ioprio
> - * in copy_process().
> - */
> read_lock(&tasklist_lock);
> switch (which) {
> case IOPRIO_WHO_PROCESS:
Attachment:
pgpcBJMkNhu3J.pgp
Description: PGP signature
