2017-12-01 21:31:47

by Sukadev Bhattiprolu

Subject: [PATCH 1/1]: powerpc: block interrupts when updating TIDR

From: Sukadev Bhattiprolu <[email protected]>
Date: Tue, 28 Nov 2017 13:39:43 -0600
Subject: [PATCH 1/1]: powerpc: block interrupts when updating TIDR

clear_thread_tidr() is called in interrupt context as a part of delayed
put of the task structure (i.e as a part of timer interrupt). To prevent
a deadlock, block interrupts when holding vas_thread_id_lock to set/
clear TIDR for a task.

Signed-off-by: Sukadev Bhattiprolu <[email protected]>
---
arch/powerpc/kernel/process.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index bfdd783..aa8dbb9 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1509,14 +1509,15 @@ static int assign_thread_tidr(void)
{
int index;
int err;
+ unsigned long flags;

again:
if (!ida_pre_get(&vas_thread_ida, GFP_KERNEL))
return -ENOMEM;

- spin_lock(&vas_thread_id_lock);
+ spin_lock_irqsave(&vas_thread_id_lock, flags);
err = ida_get_new_above(&vas_thread_ida, 1, &index);
- spin_unlock(&vas_thread_id_lock);
+ spin_unlock_irqrestore(&vas_thread_id_lock, flags);

if (err == -EAGAIN)
goto again;
@@ -1524,9 +1525,9 @@ static int assign_thread_tidr(void)
return err;

if (index > MAX_THREAD_CONTEXT) {
- spin_lock(&vas_thread_id_lock);
+ spin_lock_irqsave(&vas_thread_id_lock, flags);
ida_remove(&vas_thread_ida, index);
- spin_unlock(&vas_thread_id_lock);
+ spin_unlock_irqrestore(&vas_thread_id_lock, flags);
return -ENOMEM;
}

@@ -1535,9 +1536,11 @@ static int assign_thread_tidr(void)

static void free_thread_tidr(int id)
{
- spin_lock(&vas_thread_id_lock);
+ unsigned long flags;
+
+ spin_lock_irqsave(&vas_thread_id_lock, flags);
ida_remove(&vas_thread_ida, id);
- spin_unlock(&vas_thread_id_lock);
+ spin_unlock_irqrestore(&vas_thread_id_lock, flags);
}

/*
--
2.7.4

2018-01-29 04:15:55

by Michael Ellerman

Subject: Re: [1/1] : powerpc: block interrupts when updating TIDR

On Fri, 2017-12-01 at 21:31:40 UTC, Sukadev Bhattiprolu wrote:
> From: Sukadev Bhattiprolu <[email protected]>
> Date: Tue, 28 Nov 2017 13:39:43 -0600
> Subject: [PATCH 1/1]: powerpc: block interrupts when updating TIDR
>
> clear_thread_tidr() is called in interrupt context as a part of delayed
> put of the task structure (i.e as a part of timer interrupt). To prevent
> a deadlock, block interrupts when holding vas_thread_id_lock to set/
> clear TIDR for a task.
>
> Signed-off-by: Sukadev Bhattiprolu <[email protected]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/384dfd627f1ee67d028e6f14c6e9bf

cheers