Subject: [Bug 216041] Stack overflow at boot (do_IRQ: stack overflow: 1984) on a PowerMac G4 DP, KASAN debug build

From: [email-masked]
Date: Sat, 28 May 2022 18:50:12 +0000

https://bugzilla.kernel.org/show_bug.cgi?id=216041

Arnd Bergmann ([email-masked]) changed:

           What    |Removed                     |Added
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                 CC|                            [email-masked]

--- Comment #4 from Arnd Bergmann ([email-masked]) ---
Setting it higher is probably a good idea, but there really isn't a safe limit
with KASAN, at least if KASAN_STACK is active, running with KASAN always has a
risk of running into stack overflow issues.

One thing that sticks out is that there is an interrupt on the same stack as
the task, in 

[eaa1c800] [c0009258] do_IRQ+0x20/0x34
[eaa1c820] [c00045b4] HardwareInterrupt_virt+0x108/0x10c
[eaa1c920] [c0c59b2c] __schedule+0x3f0/0x9dc
[eaa1c9b0] [c0c5a18c] schedule+0x74/0x13c

It looks like on ppc32, as of 547db12fd8a0 ("powerpc/32: Use vmapped stacks for
interrupts"), you have either VMAP_STACK (to detect stack overflows) or IRQ
stacks (to make them less likely). I think you really want both instead, and
allocate the  IRQ stacks from vmalloc space as well.

The ext4 read path is a bit wasteful with KASAN enabled, using 1776 bytes from
ext4_lookup to ext4_read_bh, but not excessively so.

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