Date: Sun, 17 Dec 1995 23:40:03 -0800 (PST) From: David Greenman <davidg@Root.COM> To: freebsd-bugs Subject: Re: kern/901: busy pages get free'd by vm_page_free Message-ID: <199512180740.XAA08994@freefall.freebsd.org>
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The following reply was made to PR kern/901; it has been noted by GNATS.
From: David Greenman <davidg@Root.COM>
To: aagero@aage.aage.priv.no
Cc: FreeBSD-gnats-submit@freebsd.org
Subject: Re: kern/901: busy pages get free'd by vm_page_free
Date: Sun, 17 Dec 1995 23:37:12 -0800
>>Description:
>
>vm_page_free() in vfs_bio.c has an incorrent index of the free(?) pages. When
>vm_hold_free_pages() calls vm_page_free() it points to the wrong page due to
>the index being a signed datatype.
>
>>How-To-Repeat:
>
>Do a lot of activity, in order to get the paging moving. Usually ls -lR / has
>been sufficient.
>
>>Fix:
>
>Apply the included patch.
>
>--- kern/vfs_bio.c Sun Dec 17 02:51:17 1995
>+++ kern/vfs_bio.c~ Sun Dec 17 02:51:04 1995
>@@ -1634,7 +1634,7 @@
> vm_offset_t to = round_page(toa);
>
> for (pg = from; pg < to; pg += PAGE_SIZE) {
>- int index = ((caddr_t) pg - bp->b_data) >> PAGE_SHIFT;
>+ unsigned int index = ((caddr_t) pg - bp->b_data) >> PAGE_SHIFT;
> p = bp->b_pages[index];
> bp->b_pages[index] = 0;
> pmap_kremove(pg);
I must be really missing something. The index that is calculated should
always be between 0 and 1 (or some small number). I don't understand why
making index unsigned would make any difference since it should always be
positive. If it's ever negative, well then that's quite another problem.
-DG
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