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

[Sukadev Bhattiprolu]

From: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
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 <suka...@linux.vnet.ibm.com>
---
 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