Re: [PATCH] read-cache: fix division by zero core-dump

[Ben Peart <peartben@gmail.com>]

On 9/27/2018 6:24 PM, Ramsay Jones wrote:
> 
> commit 225df8a468 ("ieot: add Index Entry Offset Table (IEOT)
> extension", 2018-09-26) added a 'DIV_ROUND_UP(entries, ieot_blocks)
> expression, where ieot_blocks was set to zero for a single cpu
> platform. This caused an SIGFPE and a core dump in practically
> every test in the test-suite, until test t4056-diff-order.sh, which
> then went into an infinite loop!
> 
> Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
> ---
> 
> Hi Ben,
> 
> Could you please squash this into the relevant commits on your
> 'bp/read-cache-parallel' branch. (The first hunk fixes a sparse
> warning about using an integer as a NULL pointer).
> 

Absolutely - thanks for the patch.

I don't know how long it's been since I've been on a single core CPU - 
I'm sad for you. ;-)

> Thanks!
> 
> ATB,
> Ramsay Jones
> 
>   read-cache.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/read-cache.c b/read-cache.c
> index 6755d58877..40f096f70a 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -2141,7 +2141,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
>   	size_t extension_offset = 0;
>   #ifndef NO_PTHREADS
>   	int nr_threads, cpus;
> -	struct index_entry_offset_table *ieot = 0;
> +	struct index_entry_offset_table *ieot = NULL;
>   #endif
>   
>   	if (istate->initialized)
> @@ -2771,7 +2771,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
>   			if (ieot_blocks < 1)
>   				ieot_blocks = 1;
>   			cpus = online_cpus();
> -			if (ieot_blocks > cpus - 1)
> +			if (cpus > 1 && ieot_blocks > cpus - 1)
>   				ieot_blocks = cpus - 1;
>   		} else {
>   			ieot_blocks = nr;
>