From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Disposition: inline From: Blaisorblade Subject: Fwd: [2.6.15-rc1+ regression] do_file_page bug introduced in recent rework Date: Sat, 3 Dec 2005 04:44:12 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200512030444.12359.blaisorblade@yahoo.it> Sender: owner-linux-mm@kvack.org Return-Path: To: linux-mm@kvack.org List-ID: Fwd'ing because sent to the wrong linux-mm address. ---------- Forwarded Message ---------- Subject: [2.6.15-rc1+ regression] do_file_page bug introduced in recent rework Date: Friday 02 December 2005 01:11 From: Blaisorblade To: Hugh Dickins , Andrew Morton Cc: LKML , linux-mm@vger.kernel.org I recently found a bug introduced in your commit 65500d234e74fc4e8f18e1a429bc24e51e75de4a, i.e. between 2.6.14 and 2.6.15-rc1, about do_file_page changes wrt remap_file_pages and MAP_POPULATE. Quoting from the changelog (which is wrong): do_file_page's fallback to do_no_page dates from a time when we were testing pte_file by using it wherever possible: currently it's peculiar to nonlinear vmas, so just check that. BUG_ON if not? Better not, it's probably page table corruption, so just show the pte: hmm, there's a pte_ERROR macro, let's use that for do_wp_page's invalid pfn too. This is false: do_mmap_pgoff: if (flags & MAP_POPULATE) { up_write(&mm->mmap_sem); sys_remap_file_pages(addr, len, 0, pgoff, flags & MAP_NONBLOCK); down_write(&mm->mmap_sem); } So, with MAP_POPULATE|MAP_NONBLOCK passed, you can get a linear PAGE_FILE pte in a !VM_NONLINEAR vma. That PTE is very useless since it doesn't add any information, I know that, so avoiding that possible installation is a possible fix, but for now it's simpler to change the test in do_file_page(). Btw, in fact I discovered this bug while I was implementing this optimization (working again on remap_file_pages() patches of this summer). Indeed, the condition to test (and to possibly BUG_ON/pte_ERROR) is that ->populate must exist for the sys_remap_file_pages call to work. -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ------------------------------------------------------- -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ___________________________________ Yahoo! Mail: gratis 1GB per i messaggi e allegati da 10MB http://mail.yahoo.it -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org