pagecache: fix on-demand mapping of evicted pages #2016
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When a page fault occurs on a file-backed mapping for a page that was previously in the page cache but has later been evicted, the fault handler calls pagecache_map_page_if_filled(), which should return `false` because the newly re-allocated page has not been filled yet. Commit 132a832 introduced a regression which causes pagecache_map_page_if_filled() to return `true` instead; this leads to page cache contents inconsistent with file contents and erroneous data accessed by the user program via the file-backed mapping. This change fixes the above issue by amending the touch_or_fill_page_nodelocked() function so that it returns `false` when the relevant page is in the ALLOC state.
eyberg
approved these changes
Apr 17, 2024
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When a page fault occurs on a file-backed mapping for a page that was previously in the page cache but has later been evicted, the fault handler calls pagecache_map_page_if_filled(), which should return
falsebecause the newly re-allocated page has not been filled yet. Commit 132a832 introduced a regression which causes pagecache_map_page_if_filled() to returntrueinstead; this leads to page cache contents inconsistent with file contents and erroneous data accessed by the user program via the file-backed mapping.This change fixes the above issue by amending the touch_or_fill_page_nodelocked() function so that it returns
falsewhen the relevant page is in the ALLOC state.