Bug 217448

I'm debugging it now, I'm willing to bet that this line is causing a divide by zero:

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 0a78045ca1d9..7d9ca799f767 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2583,6 +2583,7 @@ static void spi_nor_init_default_params(struct spi_nor *nor)
    /* Set SPI NOR sizes. */
    params->writesize = 1;
    params->size = (u64)info->sector_size * info->n_sectors;
+   params->bank_size = div64_u64(params->size, info->n_banks);
    params->page_size = info->page_size;
 
    if (!(info->flags & SPI_NOR_NO_FR)) {

I'm testing this now to see if it's the case. There might be some condition under which the new n_banks member is never properly initialized.

This is indeed the cause, I'm testing a fix where the "n_banks" value is made 0 based, so that "1" is the lowest possible number and is achieved without any additional initialization.

It appears that in 6.4-rc2 the code already depends on n_banks having a 0 value that means something. So here's an easier fix. We just make sure there's no divide by zero if n_banks is 0. Testing this now...

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 0bb0ad14a2fc..084117959be4 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2921,7 +2921,10 @@ static void spi_nor_late_init_params(struct spi_nor *nor)
    if (nor->flags & SNOR_F_HAS_LOCK && !nor->params->locking_ops)
        spi_nor_init_default_locking_ops(nor);
 
-   nor->params->bank_size = div64_u64(nor->params->size, nor->info->n_banks);
+   if (nor->info->n_banks > 0)
+       nor->params->bank_size = div64_u64(nor->params->size, nor->info->n_banks);
+   else
+       nor->params->bank_size = 0;
 }

Tested and it works, I just submitted the patch to lkml:

https://marc.info/?l=linux-kernel&m=168427739123254&w=2

Created attachment 304280 [details]
0001-MTD-SPI-NOR-BUG-FIX-of-divide-by-zero-in-new-n_banks.patch

Tested extensively on the Lenovo and works well.

Hi Todd,

There is a fix landed on linux-next (79a4db50192c19 ("mtd: spi-nor: Delay the initialization of bank_size")). Can you check linux-next and see if your regression is solved?

(In reply to Bagas Sanjaya from comment #6)
> 
> There is a fix landed on linux-next

Not sure if it's a good idea to ask reporters to test linux-next, as the risk that something goes sideways there is a bit bigger than mainline. 

But well, I guess in this case it doesn't matter much, as Todd likely knowns enough about the kernel to judge for himself.

> (79a4db50192c19 ("mtd: spi-nor: Delay the initialization of bank_size")). 

Huh? That patch is already in 6.4-rc1. Did you want to copy'n'paste something else?

On 5/18/23 15:18, bugzilla-daemon@kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=217448
> 
> --- Comment #7 from The Linux kernel's regression tracker (Thorsten Leemhuis)
> (regressions@leemhuis.info) ---
> (In reply to Bagas Sanjaya from comment #6)
>>
>> There is a fix landed on linux-next
> 
> Not sure if it's a good idea to ask reporters to test linux-next, as the risk
> that something goes sideways there is a bit bigger than mainline. 
> 
> But well, I guess in this case it doesn't matter much, as Todd likely knowns
> enough about the kernel to judge for himself.
> 
>> (79a4db50192c19 ("mtd: spi-nor: Delay the initialization of bank_size")). 
> 
> Huh? That patch is already in 6.4-rc1. Did you want to copy'n'paste something
> else?
> 

I forgot to `git describe` that fix...

The patch you mentioned already appears to be in mainline, and on it's own it still has the divide by zero.

Tudor Ambarus just submitted a full patch that I've tested and verified, so hopefully that will get accepted soon.

https://marc.info/?l=linux-kernel&m=168440000825531&w=2