From 46e714c729c8d1d8110bc0545d7ffe8a759c9dc0 Mon Sep 17 00:00:00 2001 From: Suren Baghdasaryan Date: Tue, 26 Dec 2023 13:46:10 -0800 Subject: arch/mm/fault: fix major fault accounting when retrying under per-VMA lock A test [1] in Android test suite started failing after [2] was merged. It turns out that after handling a major fault under per-VMA lock, the process major fault counter does not register that fault as major. Before [2] read faults would be done under mmap_lock, in which case FAULT_FLAG_TRIED flag is set before retrying. That in turn causes mm_account_fault() to account the fault as major once retry completes. With per-VMA locks we often retry because a fault can't be handled without locking the whole mm using mmap_lock. Therefore such retries do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] because we can now handle read major faults under per-VMA lock and upon retry the fact there was a major fault gets lost. Fix this by setting FAULT_FLAG_TRIED after retrying under per-VMA lock if VM_FAULT_MAJOR was returned. Ideally we would use an additional VM_FAULT bit to indicate the reason for the retry (could not handle under per-VMA lock vs other reason) but this simpler solution seems to work, so keeping it simple. [1] https://cs.android.com/android/platform/superproject/+/master:test/vts-testcase/kernel/api/drop_caches_prop/drop_caches_test.cpp [2] https://lore.kernel.org/all/20231006195318.4087158-6-willy@infradead.org/ Link: https://lkml.kernel.org/r/20231226214610.109282-1-surenb@google.com Fixes: 12214eba1992 ("mm: handle read faults under the VMA lock") Signed-off-by: Suren Baghdasaryan Cc: Matthew Wilcox Cc: Alexander Gordeev Cc: Andy Lutomirski Cc: Catalin Marinas Cc: Christophe Leroy Cc: Dave Hansen Cc: Gerald Schaefer Cc: Michael Ellerman Cc: Palmer Dabbelt Cc: Peter Zijlstra Cc: Will Deacon Signed-off-by: Andrew Morton --- arch/s390/mm/fault.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/s390') diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c index 249aefcf7c4e..ab4098886e56 100644 --- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -337,6 +337,9 @@ static void do_exception(struct pt_regs *regs, int access) return; } count_vm_vma_lock_event(VMA_LOCK_RETRY); + if (fault & VM_FAULT_MAJOR) + flags |= FAULT_FLAG_TRIED; + /* Quick path to respond to signals */ if (fault_signal_pending(fault, regs)) { if (!user_mode(regs)) -- cgit v1.2.3