2024-06-11 03:52:30

by Gui-Dong Han

Subject: [PATCH] aoe: consolidate flags update to prevent race condition

In aoecmd_sleepwork, there is a race condition caused by two consecutive
writes to the 'flags' variable within a critical section. If a read
operation occurs between these writes, an intermediate state may be
read, potentially causing bugs.

To address this issue, the 'flags' variable should be updated in a
single operation to ensure atomicity and prevent any intermediate state
from being read.

Fixes: 3ae1c24e395b ("[PATCH] aoe [2/8]: support dynamic resizing of AoE devices")
Signed-off-by: Gui-Dong Han <[email protected]>
---
drivers/block/aoe/aoecmd.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c
index cc9077b588d7..37d556f019c0 100644
--- a/drivers/block/aoe/aoecmd.c
+++ b/drivers/block/aoe/aoecmd.c
@@ -897,8 +897,7 @@ aoecmd_sleepwork(struct work_struct *work)
set_capacity_and_notify(d->gd, d->ssize);

spin_lock_irq(&d->lock);
- d->flags |= DEVFL_UP;
- d->flags &= ~DEVFL_NEWSIZE;
+ d->flags = (d->flags | DEVFL_UP) & ~DEVFL_NEWSIZE;
spin_unlock_irq(&d->lock);
}
}
--
2.34.1

2024-06-12 16:54:44

by Jens Axboe

Subject: Re: [PATCH] aoe: consolidate flags update to prevent race condition

On 6/10/24 9:52 PM, Gui-Dong Han wrote:
> In aoecmd_sleepwork, there is a race condition caused by two consecutive
> writes to the 'flags' variable within a critical section. If a read
> operation occurs between these writes, an intermediate state may be
> read, potentially causing bugs.
>
> To address this issue, the 'flags' variable should be updated in a
> single operation to ensure atomicity and prevent any intermediate state
> from being read.
>
> Fixes: 3ae1c24e395b ("[PATCH] aoe [2/8]: support dynamic resizing of AoE devices")
> Signed-off-by: Gui-Dong Han <[email protected]>
> ---
> drivers/block/aoe/aoecmd.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c
> index cc9077b588d7..37d556f019c0 100644
> --- a/drivers/block/aoe/aoecmd.c
> +++ b/drivers/block/aoe/aoecmd.c
> @@ -897,8 +897,7 @@ aoecmd_sleepwork(struct work_struct *work)
> set_capacity_and_notify(d->gd, d->ssize);
>
> spin_lock_irq(&d->lock);
> - d->flags |= DEVFL_UP;
> - d->flags &= ~DEVFL_NEWSIZE;
> + d->flags = (d->flags | DEVFL_UP) & ~DEVFL_NEWSIZE;
> spin_unlock_irq(&d->lock);
> }

It's modified under the lock, and any reader should do so as well. If
not, there's a race regardless of your change or not.

--
Jens Axboe