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23 October 2021, 00:29:24 UTC
Revision d98c7a09843621f1b145ca5ae8ed03ff04085edb authored by Hugh Dickins on 14 February 2006, 21:52:59 UTC, committed by Linus Torvalds on 15 February 2006, 00:09:33 UTC 
[PATCH] compound page: default destructor
 
Somehow I imagined that calling a NULL destructor would free a compound page
rather than oopsing.  No, we must supply a default destructor, __free_pages_ok
using the order noted by prep_compound_page.  hugetlb can still replace this
as before with its own free_huge_page pointer.

The case that needs this is not common: rarely does put_compound_page's
put_page_testzero bring the count down to 0.  But if get_user_pages is applied
to some part of a compound page, without immediate release (e.g.  AIO or
Infiniband), then it's possible for its put_page to come after the containing
vma has been unmapped and the driver done its free_pages.

That's just the kind of case compound pages are supposed to be guarding
against (but Nick points out, nor did PageReserved handle this right).

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 parent 41d78ba
History
Tip revision: d98c7a09843621f1b145ca5ae8ed03ff04085edb authored by Hugh Dickins on 14 February 2006, 21:52:59 UTC
[PATCH] compound page: default destructor
Tip revision: d98c7a0
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