[PATCH] futex: Don't enable IRQs unconditionally in put_pi_state()

[PATCH] futex: Don't enable IRQs unconditionally in put_pi_state()

[Dan Carpenter]

The exit_pi_state_list() function calls put_pi_state() with IRQs
disabled and is not expecting that IRQs will be enabled inside the
function.  Use the _irqsave() so that IRQs are restored to the original
state instead of enabled unconditionally.

Fixes: 153fbd1226fb ("futex: Fix more put_pi_state() vs. exit_pi_state_list() races")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
This is from static analysis and not tested.  I am not very familiar
with futex code.

 kernel/futex.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index f8614ef4ff31..ca84745713bc 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -788,8 +788,9 @@ static void put_pi_state(struct futex_pi_state *pi_state)
 	 */
 	if (pi_state->owner) {
 		struct task_struct *owner;
+		unsigned long flags;
 
-		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+		raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
 		owner = pi_state->owner;
 		if (owner) {
 			raw_spin_lock(&owner->pi_lock);
@@ -797,7 +798,7 @@ static void put_pi_state(struct futex_pi_state *pi_state)
 			raw_spin_unlock(&owner->pi_lock);
 		}
 		rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
-		raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+		raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
 	}
 
 	if (current->pi_state_cache) {
-- 
2.28.0

Re: [PATCH] futex: Don't enable IRQs unconditionally in put_pi_state()

[Peter Zijlstra]

On Fri, Nov 06, 2020 at 11:52:05AM +0300, Dan Carpenter wrote:
> The exit_pi_state_list() function calls put_pi_state() with IRQs
> disabled and is not expecting that IRQs will be enabled inside the
> function.  Use the _irqsave() so that IRQs are restored to the original
> state instead of enabled unconditionally.
> 
> Fixes: 153fbd1226fb ("futex: Fix more put_pi_state() vs. exit_pi_state_list() races")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> This is from static analysis and not tested.  I am not very familiar
> with futex code.

It it exceedingly rare if at all possible to trigger this, but yes, your
patch is correct.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> 
>  kernel/futex.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index f8614ef4ff31..ca84745713bc 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -788,8 +788,9 @@ static void put_pi_state(struct futex_pi_state *pi_state)
>  	 */
>  	if (pi_state->owner) {
>  		struct task_struct *owner;
> +		unsigned long flags;
>  
> -		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
> +		raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
>  		owner = pi_state->owner;
>  		if (owner) {
>  			raw_spin_lock(&owner->pi_lock);
> @@ -797,7 +798,7 @@ static void put_pi_state(struct futex_pi_state *pi_state)
>  			raw_spin_unlock(&owner->pi_lock);
>  		}
>  		rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
> -		raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
> +		raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
>  	}
>  
>  	if (current->pi_state_cache) {
> -- 
> 2.28.0
> 

[tip: locking/urgent] futex: Don't enable IRQs unconditionally in put_pi_state()

[tip-bot2 for Dan Carpenter]

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     1e106aa3509b86738769775969822ffc1ec21bf4
Gitweb:        https://git.kernel.org/tip/1e106aa3509b86738769775969822ffc1ec21bf4
Author:        Dan Carpenter <dan.carpenter@oracle.com>
AuthorDate:    Fri, 06 Nov 2020 11:52:05 +03:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 09 Nov 2020 14:30:30 +01:00

futex: Don't enable IRQs unconditionally in put_pi_state()

The exit_pi_state_list() function calls put_pi_state() with IRQs disabled
and is not expecting that IRQs will be enabled inside the function.

Use the _irqsave() variant so that IRQs are restored to the original state
instead of being enabled unconditionally.

Fixes: 153fbd1226fb ("futex: Fix more put_pi_state() vs. exit_pi_state_list() races")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20201106085205.GA1159983@mwanda
---
 kernel/futex.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index ac32887..00259c7 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -788,8 +788,9 @@ static void put_pi_state(struct futex_pi_state *pi_state)
 	 */
 	if (pi_state->owner) {
 		struct task_struct *owner;
+		unsigned long flags;
 
-		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+		raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
 		owner = pi_state->owner;
 		if (owner) {
 			raw_spin_lock(&owner->pi_lock);
@@ -797,7 +798,7 @@ static void put_pi_state(struct futex_pi_state *pi_state)
 			raw_spin_unlock(&owner->pi_lock);
 		}
 		rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
-		raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+		raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
 	}
 
 	if (current->pi_state_cache) {