netdev - Re: [PATCH v4] tcp: Add memory barrier to tcp

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: Fri, 19 Jan 2024 20:13:12 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Salvatore Dipietro <dipiets@...zon.com>
Cc: davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org, 
	pabeni@...hat.com, netdev@...r.kernel.org, blakgeof@...zon.com, 
	alisaidi@...zon.com, benh@...zon.com, dipietro.salvatore@...il.com
Subject: Re: [PATCH v4] tcp: Add memory barrier to tcp_push()

On Fri, Jan 19, 2024 at 8:03 PM Salvatore Dipietro <dipiets@...zon.com> wrote:
>
> On CPUs with weak memory models, reads and updates performed by tcp_push
> to the sk variables can get reordered leaving the socket throttled when
> it should not. The tasklet running tcp_wfree() may also not observe the
> memory updates in time and will skip flushing any packets throttled by
> tcp_push(), delaying the sending. This can pathologically cause 40ms
> extra latency due to bad interactions with delayed acks.
>
> Adding a memory barrier in tcp_push removes the bug, similarly to the
> previous commit bf06200e732d ("tcp: tsq: fix nonagle handling").
> smp_mb__after_atomic() is used to not incur in unnecessary overhead
> on x86 since not affected.
>

> Patch has been also tested on x86 (m7i.2xlarge instance) which it is not
> affected by this issue and the patch doesn't introduce any additional
> delay.
>
> Fixes: 7aa5470c2c09 ("tcp: tsq: move tsq_flags close to sk_wmem_alloc")
> Signed-off-by: Salvatore Dipietro <dipiets@...zon.com>

SGTM, thanks.
Reviewed-by: Eric Dumazet <edumazet@...gle.com>