The patch titled Subject: proc: clear_refs: do not clear reserved pages has been added to the -mm tree. Its filename is proc-clear_refs-do-not-clear-reserved-pages.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Will Deacon <will.deacon@xxxxxxx> Subject: proc: clear_refs: do not clear reserved pages /proc/pid/clear_refs is used to clear the Referenced and YOUNG bits for pages and corresponding page table entries of the task with PID pid, which includes any special mappings inserted into the page tables in order to provide things like vDSOs and user helper functions. On ARM this causes a problem because the vectors page is mapped as a global mapping and since ec706dab ("ARM: add a vma entry for the user accessible vector page"), a VMA is also inserted into each task for this page to aid unwinding through signals and syscall restarts. Since the vectors page is required for handling faults, clearing the YOUNG bit (and subsequently writing a faulting pte) means that we lose the vectors page *globally* and cannot fault it back in. This results in a system deadlock on the next exception. To see this problem in action, just run: $ echo 1 > /proc/self/clear_refs on an ARM platform (as any user) and watch your system hang. I think this has been the case since 2.6.37 This patch avoids clearing the aforementioned bits for reserved pages, therefore leaving the vectors page intact on ARM. Since reserved pages are not candidates for swap, this change should not have any impact on the usefulness of clear_refs. Signed-off-by: Will Deacon <will.deacon@xxxxxxx> Reported-by: Moussa Ba <moussaba@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Russell King <rmk@xxxxxxxxxxxxxxxx> Cc: Nicolas Pitre <nico@xxxxxxxxxxx> Cc: Matt Mackall <mpm@xxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [2.6.37+] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/proc/task_mmu.c | 3 +++ 1 file changed, 3 insertions(+) diff -puN fs/proc/task_mmu.c~proc-clear_refs-do-not-clear-reserved-pages fs/proc/task_mmu.c --- a/fs/proc/task_mmu.c~proc-clear_refs-do-not-clear-reserved-pages +++ a/fs/proc/task_mmu.c @@ -518,6 +518,9 @@ static int clear_refs_pte_range(pmd_t *p if (!page) continue; + if (PageReserved(page)) + continue; + /* Clear accessed and referenced bits. */ ptep_test_and_clear_young(vma, addr, pte); ClearPageReferenced(page); _ Subject: Subject: proc: clear_refs: do not clear reserved pages Patches currently in -mm which might be from will.deacon@xxxxxxx are origin.patch linux-next.patch proc-clear_refs-do-not-clear-reserved-pages.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html