linux-kernel - Re: [PATCH AUTOSEL 5.10 5/7] cifs: add a warning when the in-flight count goes negative

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Message-ID: <2023082936-reborn-overjoyed-b3bc@gregkh>
Date:   Tue, 29 Aug 2023 15:47:28 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Shyam Prasad N <sprasad@...rosoft.com>,
        Bharath SM <bharathsm@...rosoft.com>,
        Steve French <stfrench@...rosoft.com>, pc@....nz,
        lsahlber@...hat.com, pc@...guebit.com, vl@...ba.org,
        ematsumiya@...e.de
Subject: Re: [PATCH AUTOSEL 5.10 5/7] cifs: add a warning when the in-flight
 count goes negative

On Tue, Aug 29, 2023 at 09:33:34AM -0400, Sasha Levin wrote:
> From: Shyam Prasad N <sprasad@...rosoft.com>
> 
> [ Upstream commit e4645cc2f1e2d6f268bb8dcfac40997c52432aed ]
> 
> We've seen the in-flight count go into negative with some
> internal stress testing in Microsoft.
> 
> Adding a WARN when this happens, in hope of understanding
> why this happens when it happens.
> 
> Signed-off-by: Shyam Prasad N <sprasad@...rosoft.com>
> Reviewed-by: Bharath SM <bharathsm@...rosoft.com>
> Signed-off-by: Steve French <stfrench@...rosoft.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  fs/cifs/smb2ops.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index 015b7b37edee5..7ed6c2d4c549a 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -82,6 +82,7 @@ smb2_add_credits(struct TCP_Server_Info *server,
>  		*val = 65000; /* Don't get near 64K credits, avoid srv bugs */
>  		pr_warn_once("server overflowed SMB3 credits\n");
>  	}
> +	WARN_ON_ONCE(server->in_flight == 0);
>  	server->in_flight--;
>  	if (server->in_flight == 0 && (optype & CIFS_OP_MASK) != CIFS_NEG_OP)
>  		rc = change_conf(server);
> -- 
> 2.40.1
> 

Please drop this from all queues, it's debugging code for the CIFS
developers, and they can debug it in Linus's tree, not in the stable
trees where something like this is going to cause systems to reboot.

thanks,

greg k-h