linux-kernel - Re: [RFC PATCH] 9p: forbid use of mempool for TFLUSH

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Message-ID: <0aa8323d-9461-a861-ac35-6952e7aeaf93@gmail.com>
Date:   Wed, 13 Jul 2022 02:39:06 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>,
        Christian Schoenebeck <linux_oss@...debyte.com>
Cc:     linux-kernel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        Greg Kurz <groug@...d.org>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Latchesar Ionkov <lucho@...kov.net>
Subject: Re: [RFC PATCH] 9p: forbid use of mempool for TFLUSH

On 7/13/22 00:17, Dominique Martinet wrote:
> TFLUSH is called while the thread still holds memory for the
> request we're trying to flush, so mempool alloc can deadlock
> there. With p9_msg_buf_size() rework the flush allocation is
> small so just make it fail if allocation failed; all that does
> is potentially leak the request we're flushing until its reply
> finally does come.. or if it never does until umount.

Why not just add separate mempools for flushes? We don't have to 
allocate memory for big payloads so they won't cost much, and then the 
IO paths will be fully mempool-ified :)