lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Mon, 11 May 2009 11:56:02 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: Q: semaphore and kmalloc(GFP_KERNEL)?

> Hello.
> I got a question.
> 
> When we use kmalloc(GFP_KERNEL), we cannot use spinlock.
> We use semaphore instead.
> 
> What happens if a writer process got into sleep state at kmalloc()
> without releasing a rw_semaphore for writing,
> 
>     down_write(&sem);
>     list_for_each()
>         ...;
>     ptr = kmalloc(size, GFP_KERNEL);
>     list_add();
>     up_write(&sem);
> 
> and then reader processes tried to hold that rw_semaphore?
> 
>     down_read(&sem);
>     list_for_each()
>         ...;
>     up_read(&sem);
> 
> Can the kernel detect that we need to let kmalloc() fail and
> wake up the writer process so that the writer process releases
> the rw_semaphore and reader processes can continue?

it can't. Plus it shouldn't.
some caller don't want kmalloc() failure.


> (If the kernel can't detect, I worry that we experience
> all processes sleeping for undefined duration.)




--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists