linux-kernel - Re: [V9fs-developer] KCSAN BUG report on p9_client_cb / p9_client

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Date:   Wed, 23 Jun 2021 02:12:54 +0900
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     jim.cromie@...il.com
Cc:     kasan-dev@...glegroups.com, v9fs-developer@...ts.sourceforge.net,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [V9fs-developer] KCSAN BUG report on p9_client_cb / p9_client_rpc

jim.cromie@...il.com wrote on Tue, Jun 22, 2021 at 10:42:58AM -0600:
> I got this on rc7 + my hacks ( not near p9 )
> ISTM someone here will know what it means.
> If theres anything else i can do to help,
> (configs, drop my patches and retry)
>  please let me know

Thanks for the report!

> [   14.904783] ==================================================================
> [   14.905848] BUG: KCSAN: data-race in p9_client_cb / p9_client_rpc

hm, this code hasn't changed in ages (unless someone merged code behind
my back :D)

I had assumed the p9_req_put() in p9_client_cb would protect the tag,
but that doesn't appear to be true -- could you try this patch if this
is reproductible to you?

The tag is actually reclaimed in the woken up p9_client_rpc thread so
that would be a good match (reset in the other thread vs. read here),
caching the value is good enough but that is definitely not obvious...

-- 
Dominique

View attachment "0001-9p-net-cache-tag-in-p9_client_cb.patch" of type "text/plain" (1398 bytes)