linux-kernel - Re: [PATCH 2/2] module: add support to avoid duplicates early on load

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Date:   Thu, 25 May 2023 17:42:10 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Petr Pavlu <petr.pavlu@...e.com>,
        Luis Chamberlain <mcgrof@...nel.org>
Cc:     rafael@...nel.org, song@...nel.org, lucas.de.marchi@...il.com,
        lucas.demarchi@...el.com, christophe.leroy@...roup.eu,
        peterz@...radead.org, rppt@...nel.org, dave@...olabs.net,
        willy@...radead.org, vbabka@...e.cz, mhocko@...e.com,
        dave.hansen@...ux.intel.com, colin.i.king@...il.com,
        jim.cromie@...il.com, catalin.marinas@....com, jbaron@...mai.com,
        rick.p.edgecombe@...el.com, yujie.liu@...el.com, david@...hat.com,
        tglx@...utronix.de, hch@....de, patches@...ts.linux.dev,
        linux-modules@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, pmladek@...e.com, prarit@...hat.com,
        lennart@...ttering.net
Subject: Re: [PATCH 2/2] module: add support to avoid duplicates early on load

On Thu, May 25, 2023 at 09:07:23AM -0700, Linus Torvalds wrote:
> > It means that these and similarly organized distributions end up using
> > init_module(), and adding complexity to optimize finit_module() wouldn't
> > actually help in their case.
> 
> Yeah, I think the real bug is absolutely in udev, and trying to load
> the same module hundreds of times is very very wrong. So I think the
> "mitigate it in the kernel" is at most a quick hack to fix user-space
> brokenness.

I totally agree.  I also agree that this doesn't really seem to be any
sort of "bug" in that no memory leaks, and when userspace calms down,
all goes back to normal.  So hacks in the vfs layer for this is not
good, let's not paper over userspace code that we have control over with
kernel changes.

Luis, I asked last time what modules are being asked by the kernel to be
loaded thousands of times at boot and can't seem to find an answer
anywhere, did I miss that?  This should be very easy to handle in
userspace if systems need it, so that begs the questions, what types of
systems need this?  We have handled booting with tens of thousands of
devices attached for decades now with no reports of boot/udev/kmod
issues before, what has recently changed to cause issues?

thanks,

greg k-h