英文:
Check Linux Pagecache Entry Validity
问题
我使用find_get_entries()来检索与所有打开的文件相关联的pagecache页面。对于每个检索到的页面，将需要调用put_page()来将页面的引用计数恢复到其先前的状态。find_get_entries()似乎存在竞争条件。在某些情况下，返回的struct page *元素包含垃圾（可能是因为与索引相关联的页面已被驱逐）。因此，在这种页面上调用put_page()将导致内核崩溃。我该如何避免这种情况？
英文:
I used find_get_entries() to retrieve pagecache pages associated with all opened files. For each retrieved page, a put_page() invocation will be needed to revert the page reference count to its previous state. find_get_entries() seems to be racy. In some scenarios, the returned struct page * element contains garbage (perhaps because the page associated with an index has been evicted). Therefore, a put_page() call on such a page will cause kernel panic. How can I avoid this situation?
答案1
得分: 1
似乎最近被驱逐页面的阴影条目等（通过调用xa_is_value()识别）也将在entries参数中返回。可以通过检查它们的LSB（即，如果（unsigned long）entries[i]＆1不为零，则该元素不是有效页面）来识别并忽略它们。
英文:
It seems that the shadow entries of recently evicted pages, etc. (recognized by calling xa_is_value()) will also be returned in the entries parameter. They can be identified and ignored by checking their LSB (i.e., if (unsigned long)entries[i] & 1 is not zero, the element is not a valid page).
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