Messages in this thread | | | Date | Tue, 1 Mar 2016 14:16:56 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH] mm: __delete_from_page_cache show Bad page if mapped |
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On Mon, Feb 29, 2016 at 10:45:59PM -0800, Hugh Dickins wrote: > Commit e1534ae95004 ("mm: differentiate page_mapped() from page_mapcount() > for compound pages") changed the famous BUG_ON(page_mapped(page)) in > __delete_from_page_cache() to VM_BUG_ON_PAGE(page_mapped(page)): which > gives us more info when CONFIG_DEBUG_VM=y, but nothing at all when not. > > Although it has not usually been very helpul, being hit long after the > error in question, we do need to know if it actually happens on users' > systems; but reinstating a crash there is likely to be opposed :) > > In the non-debug case, pr_alert("BUG: Bad page cache") plus dump_page(), > dump_stack(), add_taint() - I don't really believe LOCKDEP_NOW_UNRELIABLE, > but that seems to be the standard procedure now. Move that, or the > VM_BUG_ON_PAGE(), up before the deletion from tree: so that the > unNULLified page->mapping gives a little more information. > > If the inode is being evicted (rather than truncated), it won't have > any vmas left, so it's safe(ish) to assume that the raised mapcount is > erroneous, and we can discount it from page_count to avoid leaking the > page (I'm less worried by leaking the occasional 4kB, than losing a > potential 2MB page with each 4kB page leaked). > > Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
-- Kirill A. Shutemov
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