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Code Issues Releases Activity

Fix a bug in the new madvise() code that would possibly (improperly)

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free swap space out from under a busy page.  This is not legal because
    the swap may be reallocated and I/O issued while I/O is still in
    progress on the same swap page from the madvise()'d object.  This bug
    could only occur under extreme paging conditions but might not cause
    an error until much later.  As a side-benefit, madvise() is now even
    smaller.
This commit is contained in:
Matthew Dillon 1999-02-15 02:03:40 +00:00
parent e430ec940a
commit 1ce137be82
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=44034
1 changed files with 12 additions and 24 deletions
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36
sys/vm/vm_object.c
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@ -61,7 +61,7 @@
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*
* $Id: vm_object.c,v 1.149 1999/02/12 09:51:43 dillon Exp $
* $Id: vm_object.c,v 1.150 1999/02/12 20:42:19 dillon Exp $
*/
/*
@ -761,29 +761,6 @@ vm_object_madvise(object, pindex, count, advise)
end = pindex + count;
/*
* MADV_FREE special case - free any swap backing store now,
* whether or not resident pages can be found later.
*/
if (advise == MADV_FREE) {
tobject = object;
tpindex = pindex;
while (
(tobject->type == OBJT_DEFAULT ||
tobject->type == OBJT_SWAP) &&
(tobject->flags & OBJ_ONEMAPPING)
) {
if (tobject->type == OBJT_SWAP) {
swap_pager_freespace(tobject, tpindex, count);
}
if ((tobject = tobject->backing_object) == NULL)
break;
tpindex += OFF_TO_IDX(tobject->backing_object_offset);
}
}
/*
* Locate and adjust resident pages
*/
@ -806,6 +783,15 @@ vm_object_madvise(object, pindex, count, advise)
m = vm_page_lookup(tobject, tpindex);
if (m == NULL) {
/*
* There may be swap even if there is no backing page
*/
if (advise == MADV_FREE && tobject->type == OBJT_SWAP)
swap_pager_freespace(tobject, tpindex, 1);
/*
* next object
*/
tobject = tobject->backing_object;
if (tobject == NULL)
continue;
@ -853,6 +839,8 @@ vm_object_madvise(object, pindex, count, advise)
m->dirty = 0;
m->act_count = 0;
vm_page_deactivate(m);
if (tobject->type == OBJT_SWAP)
swap_pager_freespace(tobject, tpindex, 1);
}
}
}