Re: [PATCH] spi: bcm2835: do not unregister controller in shutdown handler

[Mark Brown <broonie@kernel.org>]

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On Tue, Sep 28, 2021 at 09:56:57PM +0200, Lino Sanfilippo wrote:
> Do not unregister the SPI controller in the shutdown handler. The reason
> to avoid this is that controller unregistration results in the slave
> devices remove() handler being called which may be unexpected for slave
> drivers at system shutdown.
> 
> One example is if the BCM2835 driver is used together with the TPM SPI
> driver:
> At system shutdown first the TPM chip devices (pre) shutdown handler
> (tpm_class_shutdown) is called, stopping the chip and setting an operations
> pointer to NULL.
> Then since the BCM2835 shutdown handler unregisters the SPI controller the
> TPM SPI remove function (tpm_tis_spi_remove) is also called. In case of
> TPM 2 this function accesses the now nullified operations pointer,
> resulting in the following NULL pointer access:
> 
> [  174.078277] 8<--- cut here ---
> [  174.078288] Unable to handle kernel NULL pointer dereference at virtual address 00000034
> [  174.078293] pgd = 557a5fc9
> [  174.078300] [00000034] *pgd=031cf003, *pmd=00000000
> [  174.078317] Internal error: Oops: 206 [#1] SMP ARM
> [  174.078323] Modules linked in: tpm_tis_spi tpm_tis_core tpm spidev gpio_pca953x mcp320x rtc_pcf2127 industrialio regmap_i2c regmap_spi 8021q garp stp llc ftdi_sio6

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message. If part of the backtrace is usefully illustrative (it often is
for search engines if nothing else) then it's usually better to pull out
the relevant sections.

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