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

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Message-ID: <87y1hr22o1.fsf@mail.lhotse>
Date:   Thu, 31 Aug 2023 15:37:02 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Andreas Schwab <schwab@...ux-m68k.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 1/2] maple_tree: Disable mas_wr_append() when other
 readers are possible

Andreas Schwab <schwab@...ux-m68k.org> writes:
> This breaks booting on ppc32:

Does enabling CONFIG_DEBUG_ATOMIC_SLEEP fix the crash? It did for me on
qemu.

cheers

> Kernel attemptd to writ user page (1ff0) - exploit attempt? (uid: 0)
> BUG: Unable to handle kernel data access on write at 0x00001ff0
> Faulting instruction address: 0xc0009554
> Vector: 300 (Data Access) at [c0b09d10]
>     pc: c0009554: do_softirq_own_stack+0x18/0x30
>     lr: c004f480: __irq_exit_rcu+0x70/0xc0
>     sp: c0b09dd0
>    msr: 1032
>    dar: 1ff0
>  dsisr: 42000000
>   current = 0xc0a08360
>     pid   = 0, comm = swapper
> Linux version 6.5.0 ...
> enter ? for help
> [c0b09de0] c00ff480 __irq_exit_rcu+0x70/0xc0
> [c0b09df0] c0005a98 Decrementer_virt+0x108/0x10c
> --- Exception: 900 (Decrementer) at c06cfa0c __schedule+0x4fc/0x510
> [c0b09ec0] c06cf75c __schedule+0x1cc/0x510 (unreliable)
> [c0b09ef0] c06cfc90 __cond_resched+0x2c/0x54
> [c0b09f00] c06d07f8 mutex_lock_killable+0x18/0x5c
> [c0b09f10] c013c404 pcpu_alloc+0x110/0x4dc
> [c0b09f70] c000cc34 alloc_descr.isra.18+0x48/0x144
> [c0b09f90] c0988aa0 early_irq_init+0x64/0x8c
> [c0b09fa0] c097a5a4 start_kernel+0x5b4/0x7b0
> [c0b09ff0] 00003dc0
> mon>
>
> -- 
> Andreas Schwab, schwab@...ux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
> "And now for something completely different."