linux-kernel - Re: [RFC][PATCH v2 19/31] timers: net: Use del_timer

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Date:   Fri, 28 Oct 2022 15:46:17 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Mirko Lindner <mlindner@...vell.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Pavel Begunkov <asml.silence@...il.com>,
        Menglong Dong <imagedong@...cent.com>,
        linux-usb@...r.kernel.org, linux-wireless@...r.kernel.org,
        bridge@...ts.linux-foundation.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, lvs-devel@...r.kernel.org,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [RFC][PATCH v2 19/31] timers: net: Use del_timer_shutdown()
 before freeing timer

On Fri, 28 Oct 2022 18:31:49 -0400 Steven Rostedt wrote:
> Could someone from networking confirm (or deny) that the timer being
> removed in sk_stop_timer() will no longer be used even if del_timer()
> returns false?
> 
> net/core/sock.c:
> 
> void sk_stop_timer(struct sock *sk, struct timer_list* timer)
> {
> 	if (del_timer(timer))
> 		__sock_put(sk);
> }
> 
> If this is the case, then I'll add the following interface:
> 
>    del_timer_sync_shutdown() // the common case which syncs
> 
>    del_timer_shutdown() // the uncommon case, that returns immediately
>                         // used for those cases that add extra code to
>                         // handle it, like sk_stop_timer()

Sorry too many bugs at once :)

FWIW Paolo was saying privately earlier today that he spotted some cases
of reuse, he gave an example of ccid2_hc_tx_packet_recv()

So we can't convert all cases of sk_stop_timer() in one fell swoop :(

> Which has the same semantics as del_timer_sync() and del_timer()
> respectively, but will prevent the timer from being rearmed again.
> 
> This way we can convert the sk_stop_timer() to:
> 
> void sk_stop_timer(struct sock *sk, struct timer_list* timer)
> {
> 	if (del_timer_shutdown(timer))
> 		__sock_put(sk);
> }
> 
> 
> We can also add the del_timer_shutdown() to other locations that need to
> put a timer into a shutdown state before freeing, and where it's in a
> context that can not call del_timer_sync_shutdown().