netdev - Re: [PATCH] sock: Make sock->sk

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Message-Id: <20181222.150333.1964216452010509730.davem@davemloft.net>
Date:   Sat, 22 Dec 2018 15:03:33 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     deepa.kernel@...il.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        viro@...iv.linux.org.uk, arnd@...db.de, y2038@...ts.linaro.org
Subject: Re: [PATCH] sock: Make sock->sk_tstamp thread-safe

From: Deepa Dinamani <deepa.kernel@...il.com>
Date: Fri, 21 Dec 2018 12:27:33 -0800

> Al Viro mentioned that there is probably a race condition
> lurking in accesses of sk_tstamp on 32-bit machines.
> 
> sock->sk_tstamp is of type ktime_t which is always an s64.
> On a 32 bit architecture, we might run into situations of
> unsafe access as the access to the field becomes non atomic.
> 
> Use seqlocks for synchronization.
> This allows us to avoid using spinlocks for readers as
> readers do not need mutual exclusion.
> 
> Another approach to solve this is to require sk_lock for all
> modifications of the timestamps. The current approach allows
> for timestamps to have their own lock: sk_tstamp_lock.
> This allows for the patch to not compete with already
> existing critical sections, and side effects are limited
> to the paths in the patch.
> 
> The addition of the new field maintains the data locality
> optimizations from
> commit 9115e8cd2a0c ("net: reorganize struct sock for better data
> locality")
> 
> Note that all the instances of the sk_tstamp accesses
> are either through the ioctl or the syscall recvmsg.
> 
> Signed-off-by: Deepa Dinamani <deepa.kernel@...il.com>

Since, regardless of whether this is the final approach we will
take, it seems that sunrpc needs to be added to this patch.

So I'm definitely waiting for a new version.

Thanks.