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Date: Wed, 27 Aug 2014 11:06:29 +0100 From: David Vrabel <david.vrabel@...rix.com> To: Chen Gang <gang.chen.5i5j@...il.com> CC: <konrad.wilk@...cle.com>, <boris.ostrovsky@...cle.com>, <xen-devel@...ts.xenproject.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] drivers/xen/grant-table.c: Be sure of unsigned value never comparing with 0 On 26/08/14 20:42, Chen Gang wrote: > On 08/27/2014 01:03 AM, David Vrabel wrote: >> On 26/08/14 16:38, Chen Gang wrote: >>> In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may >>> be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than >>> 'nr_glist_frames' in failure processing, which cause infinite looping. >> >> nr_grant_frames is at least 1. See gnttab_init(). >> > > OK, thanks, that sounds reasonable to me, it is not a real wold bug, it > is my fault. :-) > >>> --- a/drivers/xen/grant-table.c >>> +++ b/drivers/xen/grant-table.c >>> @@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames) >>> return 0; >>> >>> grow_nomem: >>> - for ( ; i >= nr_glist_frames; i--) >>> - free_page((unsigned long) gnttab_list[i]); >>> + while (i > nr_glist_frames) >>> + free_page((unsigned long) gnttab_list[--i]); >> >> while (i-- > nr_glist_frames) >> ... >> >> Would have been better. >> > > OK, thanks, that sounds reasonable to me. > > If necessary to send patch v2 (change comments and contents), please > let me know, and I shall send. Applied to devel/for-linus-3.18 with this description: xen/grant-table: refactor error cleanup in grow_gnttab_list() The cleanup loop in grow_gnttab_list() is safe from the underflow of the unsigned 'i' since nr_glist_frames is >= 1, but refactor it anyway. Thanks. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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