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- Correct a long-standing race condition in vm_page_try_to_cache() that

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could result in a panic "vm_page_cache: caching a dirty page, ...":
   Access to the page must be restricted or removed before calling
   vm_page_cache().  This race condition is identical in nature to that
   which was addressed by vm_pageout.c's revision 1.251.
 - Simplify the code surrounding the fix to this same race condition
   in vm_pageout.c's revision 1.251.  There should be no behavioral
   change.  Reviewed by: tegge

MFC after:	7 days
This commit is contained in:
Alan Cox 2004-02-14 08:54:37 +00:00
parent b662bdc270
commit 84d98bf699
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=125798
2 changed files with 3 additions and 4 deletions
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2
sys/vm/vm_page.c
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@ -1292,7 +1292,7 @@ vm_page_try_to_cache(vm_page_t m)
(m->flags & (PG_BUSY|PG_UNMANAGED))) {
return (0);
}
vm_page_test_dirty(m);
pmap_remove_all(m);
if (m->dirty)
return (0);
vm_page_cache(m);

5
sys/vm/vm_pageout.c
View File

@ -801,8 +801,7 @@ vm_pageout_scan(int pass)
* far as the VM code knows, any partially dirty pages are
* fully dirty.
*/
if (m->dirty == 0) {
vm_page_test_dirty(m);
if (m->dirty == 0 && !pmap_is_modified(m)) {
/*
* Avoid a race condition: Unless write access is
* removed from the page, another processor could
@ -816,7 +815,7 @@ vm_pageout_scan(int pass)
* to the page, removing all access will be cheaper
* overall.
*/
if (m->dirty == 0 && (m->flags & PG_WRITEABLE) != 0)
if ((m->flags & PG_WRITEABLE) != 0)
pmap_remove_all(m);
} else {
vm_page_dirty(m);