Messages in this thread | | | Date | Mon, 16 Feb 2015 10:49:43 -0800 | From | Guenter Roeck <> | Subject | Re: [PATCH 1/1] kernel/fork.c: avoid division by zero |
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On 02/16/2015 10:45 AM, Heinrich Schuchardt wrote: > I am resending this mail because the linux-kernel list was not CCed. > Yes, sorry, that got lost. The "forward" feature on lkml.org doesn't work as well as it used to, unfortunately, and I keep forgetting.
> On 16.02.2015 19:23, Guenter Roeck wrote: >> On Mon, Feb 16, 2015 at 07:00:44PM +0100, Heinrich Schuchardt wrote: >>> PAGE_SIZE is not guaranteed to be equal to or less than 8 times the >>> THREAD_SIZE. >>> >>> E.g. architecture hexagon may have page size 1M and thread size 4096. >>> >>> This would lead to a division by zero. >>> >>> Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de> >>> --- >>> kernel/fork.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/kernel/fork.c b/kernel/fork.c >>> index cf65139..71e2583 100644 >>> --- a/kernel/fork.c >>> +++ b/kernel/fork.c >>> @@ -273,7 +273,8 @@ void __init fork_init(unsigned long mempages) >>> * value: the thread structures can take up at most half >>> * of memory. >>> */ >>> - max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); >>> + max_threads = (u64) PAGE_SIZE * (u64) mempages >>> + / (u64) THREAD_SIZE / 8UL; >> >> How about >> max_threads = mempages / (8 * THREAD_SIZE) * PAGE_SIZE; >> >> instead ? That would avoid the u64. > > We have to consider the case mempages < 8 * THREAD_SIZE. > > Let > mempages = 1024 > THREAD_SIZE = 4096 > PAGE_SIZE = 1M > > Your code gives 0. > Mine gives 8192. > Makes sense.
Thanks, Guenter
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