linux-kernel - Re: [PATCH] cifs: Remove locking in smb2_verify_signature() when calculating SMB2/SMB3 signature on receiving packets

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Date:   Thu, 26 Mar 2020 10:56:25 +0100
From:   Aurélien Aptel <aaptel@...e.com>
To:     longli@...uxonhyperv.com, Steve French <sfrench@...ba.org>,
        linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
        linux-kernel@...r.kernel.org
Cc:     Long Li <longli@...rosoft.com>
Subject: Re: [PATCH] cifs: Remove locking in smb2_verify_signature() when
 calculating SMB2/SMB3 signature on receiving packets

longli@...uxonhyperv.com writes:
> On the sending and receiving paths, CIFS uses the same cypto data structures
> to calculate SMB2/SMB3 packet signatures. A lock on the receiving path is
> necessary to control shared access to crypto data structures. This lock
> degrades performance because it races with the sending path.
>
> Define separate crypto data structures for sending and receiving paths and
> remove this lock.

Something I've often wondered: why do we keep crypto state in the server
structure instead of creating it as needed in the caller stack (thus
avoiding the need for locks). AFAIK there's no state that need to be
kept between signing/encrypting calls beside the access to keys. Is it that
expensive to create/release?

Cheers,
-- 
Aurélien Aptel / SUSE Labs Samba Team
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