[PATCH v3 3/7] mtd: spi-nor: Add support for panic writes

[sashiko-bot at kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] mtd: spi-nor: kmalloc/kfree during panic write causes deadlock
--

commit 3bd35bd5922a50a6d084d4da3c21aebcee2351cd
Author: Tanmay Jagdale <tanmay at marvell.com>

mtd: spi-nor: Add support for panic writes

This commit introduces the functionality for SPI NOR controllers to perform
panic writes. It attempts to bypass locked mutexes and sleep operations
when doing a panic write, since preemption and IRQs are disabled.

> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 58257cc21c681..d5e572287bb73 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
[ ... ]
> @@ -2203,7 +2242,8 @@ static int spi_nor_octal_dtr_write(struct spi_nor *nor, loff_t to, size_t len,
>  	if (IS_ALIGNED(to, 2) && IS_ALIGNED(len, 2))
>  		return spi_nor_write_data(nor, to, len, buf);
>  
> -	tmp_buf = kmalloc(nor->params->page_size, GFP_KERNEL);
> +	tmp_buf = kmalloc(nor->params->page_size,
> +			  nor->mtd.oops_panic_write ? GFP_ATOMIC : GFP_KERNEL);

[Severity: High]
Can this kmalloc() call in spi_nor_octal_dtr_write(), and the subsequent
kfree(), cause a deadlock during a panic?

While GFP_ATOMIC prevents the scheduler from sleeping or reclaiming memory,
the SLUB/SLAB memory allocator still fundamentally relies on raw spinlocks
(e.g., kmem_cache_node->list_lock or pcp->lock) for its freelists.

Since spi_nor_panic_write() is invoked in a panic context where local
interrupts are disabled and all other CPUs have been forcibly halted, if
any halted CPU happened to be holding a slab lock at the moment of the
crash, the panicking CPU will spin indefinitely waiting for it.

Should this panic path rely on a pre-allocated buffer (such as
nor->bouncebuf) instead to guarantee the panic dump can be written?

>  	if (!tmp_buf)
>  		return -ENOMEM;
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261014154301.157755-1-paul.cercueil@bootlin.com?part=3