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
| ||
|
Date: Mon, 7 May 2007 14:34:20 +0400 From: Oleg Nesterov <oleg@...sign.ru> To: Jarek Poplawski <jarkao2@...pl> Cc: Andrew Morton <akpm@...ux-foundation.org>, David Chinner <dgc@....com>, David Howells <dhowells@...hat.com>, Gautham Shenoy <ego@...ibm.com>, Ingo Molnar <mingo@...e.hu>, Srivatsa Vaddagiri <vatsa@...ibm.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] make-cancel_rearming_delayed_work-reliable-fix On 05/07, Jarek Poplawski wrote: > > There is a lot of new things in the final version of this > patch. I guess, there was no such problem in the previous > version. No, this is basically the same patch + re-check-cwq-after-lock, the latter is mostly needed to prevent racing with CPU-hotplug. > I can also see you have new doubts about usefulness, which > I cannot understand: > - even if there are some slowdowns, where does it matter? > - the "old" method uses only one method of cancelling, i.e. > del_timer, not trying to stop requeuing or to remove from > the queue; it seems to be effective only with long delayed > timers, and its real problems are probably mostly invisible. The slowdown is small, changelog mentions it just to be "fair". I am not happy with the complication this patch adds, mostly I hate this smb_wmb() in insert_work(). I have an idea how to remove it later, but this needs another patch not related to workqueue.c. > BTW, I'm still not convinced all additions are needed: > the "old" cancel_rearming_ doesn't care about checking > or waiting on anything after del_timer positive. It would be very strange to do wait_on_work() only in case when del_timer() failed. This way we still need to do cancel_work_sync() after cancel_rearming_delayed_work(), but only when del_timer() failed, ugly. Note also that wait_on_work() does not sleep if work->func() is not running. Also, consider this callback: void work_handler(struct work_struct *w) { struct delayed_work dw = container_of(...); queue_delayed_work(dw, delay); // <------------- cancel_rearming_delayed_work() cancel_delayed_work(dw); queue_delayed_work(dw, another_delay); } Yes, this is strange and ugly. But correct! The current version (before this patch) can't cancel this delayed_work. The new implementation works correctly. So I think it is far better to do wait_on_work() unconditionally. > PS: I'll try to check this all in the evening and will > write tomorrow, if found something interesting. Yes, please! Oleg. - 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