linux-kernel - Re: [PATCH v2 1/2] maple_tree: Disable mas_wr_append() when other readers are possible

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Message-ID: <f12ba12c-4625-1b13-a0c8-376138d94b45@csgroup.eu>
Date:   Tue, 12 Sep 2023 17:02:23 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "paulmck@...nel.org" <paulmck@...nel.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        Shanker Donthineni <sdonthineni@...dia.com>
Subject: Re: [PATCH v2 1/2] maple_tree: Disable mas_wr_append() when other
 readers are possible



Le 12/09/2023 à 18:49, Paul E. McKenney a écrit :
> On Tue, Sep 12, 2023 at 11:44:23AM -0400, Liam R. Howlett wrote:
>>> So my question is why is it useful to setup interrupts that early, given
>>> that interrupts cannot possibly happen until the boot CPU enables them?
>>
>> I don't know for sure, but there are 'preallocated IRQs' which end up
>> grouped 0-15, then I see another one added at 55 after the mpic console
>> output.  I suspect it's so that they can be added as they are discovered
>> during early boot?
> 
> Christophe argues that the interrupt stacks must be allocated early
> on, and that this acquires a mutex.
> 

Well, we can probably allocate them later than it is today.

In commit 547db12fd8a0 ("powerpc/32: Use vmapped stacks for interrupts") 
I already pushed the allocation at a later stage than it initialy was.

We can probably do it later if it helps, however it definitely needs to 
be done before enabling IRQs for obvious reasons, so it is a problem 
that alloc_vm_stack() calling __vmalloc_node() enables IRQs.

Christophe