From 340430c572f7b2b275d39965e88bafa71693cb23 Mon Sep 17 00:00:00 2001 From: Pekka Paalanen Date: Tue, 24 Feb 2009 21:44:15 +0200 Subject: [PATCH] x86 mmiotrace: fix race with release_kmmio_fault_page() There was a theoretical possibility to a race between arming a page in post_kmmio_handler() and disarming the page in release_kmmio_fault_page(): cpu0 cpu1 ------------------------------------------------------------------ mmiotrace shutdown enter release_kmmio_fault_page fault on the page disarm the page disarm the page handle the MMIO access re-arm the page put the page on release list remove_kmmio_fault_pages() fault on the page page not known to mmiotrace fall back to do_page_fault() *KABOOM* (This scenario also shows the double disarm case which is allowed.) Fixed by acquiring kmmio_lock in post_kmmio_handler() and checking if the page is being released from mmiotrace. Signed-off-by: Pekka Paalanen Cc: Stuart Bennett Cc: Steven Rostedt Signed-off-by: Ingo Molnar --- arch/x86/mm/kmmio.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c index 4c66bd3..9f20503 100644 --- a/arch/x86/mm/kmmio.c +++ b/arch/x86/mm/kmmio.c @@ -38,7 +38,8 @@ struct kmmio_fault_page { /* * Number of times this page has been registered as a part * of a probe. If zero, page is disarmed and this may be freed. - * Used only by writers (RCU). + * Used only by writers (RCU) and post_kmmio_handler(). + * Protected by kmmio_lock, when linked into kmmio_page_table. */ int count; }; @@ -317,7 +318,11 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs) if (ctx->probe && ctx->probe->post_handler) ctx->probe->post_handler(ctx->probe, condition, regs); - arm_kmmio_fault_page(ctx->fpage); + /* Prevent racing against release_kmmio_fault_page(). */ + spin_lock(&kmmio_lock); + if (ctx->fpage->count) + arm_kmmio_fault_page(ctx->fpage); + spin_unlock(&kmmio_lock); regs->flags &= ~X86_EFLAGS_TF; regs->flags |= ctx->saved_flags; -- 2.7.4