[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] BUG: using smp_processor_id() in preemptible [00000000] code: blkback.1.xvdb/9138 caller is decrease_reservation
On 11/09/13 13:08, Stefano Stabellini wrote: > On Wed, 11 Sep 2013, David Vrabel wrote: >> On 10/09/13 19:13, Sander Eikelenboom wrote: >>> Hi Wei, >>> >>> Just back from holiday i tried running a new xen-unstable and >>> linux kernel (current Linus his tree + Konrad's last pull request >>> merged on top). I saw a thread and patch about a bug_on in >>> increase_reservation ... i'm seeing the splat below in dom0 when >>> guests get started. >> >> Yes, the use of __per_cpu() in decrease_reservation is not safe. >> >> Stefano, what testing did you give "xen/balloon: set a mapping for >> ballooned out pages" (cd9151e2). The number of critical problems >> it's had suggests not a lot? >> >> I'm also becoming less happy with the inconsistency between the >> p2m updates between the different (non-)auto_translated_physmap >> guest types. >> >> I think it (and all the attempts to fix it) should be reverted at >> this stage and we should try again for 3.13 which some more through >> testing and a more careful look at what updates to the p2m are >> needed. > > Issues like this one are due to different kernel configurations / > usage patters. To reproduce this issue one needs a preemptible kernel > and blkback. I use a non-preemptible kernel and QEMU as block > backend. > > Granted, in this case I should have tested blkback and both > preemptible and non-preemptible kernel configurations. But in > general it is nearly impossible to test all the possible > configurations beforehand, it is a classic case of combinatorial > explosion. > > These are exactly the kind of things that an exposure to a wider > range of users/developers help identify and fix. > > So I think that we did the right thing here, by sending a pull > request early in the release cycle, so that now we have many other > RCs to fix all the issues that come up. That sounds fair. Sander, does the follow patch fix this issue? 8<--------------------------------------------------- xen/balloon: ensure preemption is disabled when using a scratch page In decrease_reservation(), if the kernel is preempted between updating the mapping and updating the p2m then they may end up using different scratch pages. Use get_balloon_scratch_page() and put_balloon_scratch_page() which use get_cpu_var() and put_cpu_var() to correctly disable preemption. Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx> --- diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index 3101cf6..a74647b 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -305,6 +305,18 @@ static enum bp_state reserve_additional_memory(long credit) } #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */ +struct page *get_balloon_scratch_page(void) +{ + struct page *ret = get_cpu_var(balloon_scratch_page); + BUG_ON(ret == NULL); + return ret; +} + +void put_balloon_scratch_page(void) +{ + put_cpu_var(balloon_scratch_page); +} + static enum bp_state increase_reservation(unsigned long nr_pages) { int rc; @@ -380,6 +392,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) enum bp_state state = BP_DONE; unsigned long pfn, i; struct page *page; + struct page *scratch_page; int ret; struct xen_memory_reservation reservation = { .address_bits = 0, @@ -399,6 +412,8 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) if (nr_pages > ARRAY_SIZE(frame_list)) nr_pages = ARRAY_SIZE(frame_list); + scratch_page = get_balloon_scratch_page(); + for (i = 0; i < nr_pages; i++) { page = alloc_page(gfp); if (page == NULL) { @@ -416,7 +431,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) if (xen_pv_domain() && !PageHighMem(page)) { ret = HYPERVISOR_update_va_mapping( (unsigned long)__va(pfn << PAGE_SHIFT), - pfn_pte(page_to_pfn(__get_cpu_var(balloon_scratch_page)), + pfn_pte(page_to_pfn(scratch_page), PAGE_KERNEL_RO), 0); BUG_ON(ret); } @@ -432,14 +447,14 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) pfn = mfn_to_pfn(frame_list[i]); if (!xen_feature(XENFEAT_auto_translated_physmap)) { unsigned long p; - struct page *pg; - pg = __get_cpu_var(balloon_scratch_page); - p = page_to_pfn(pg); + p = page_to_pfn(scratch_page); __set_phys_to_machine(pfn, pfn_to_mfn(p)); } balloon_append(pfn_to_page(pfn)); } + put_balloon_scratch_page(); + set_xen_guest_handle(reservation.extent_start, frame_list); reservation.nr_extents = nr_pages; ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation); @@ -491,18 +506,6 @@ static void balloon_process(struct work_struct *work) mutex_unlock(&balloon_mutex); } -struct page *get_balloon_scratch_page(void) -{ - struct page *ret = get_cpu_var(balloon_scratch_page); - BUG_ON(ret == NULL); - return ret; -} - -void put_balloon_scratch_page(void) -{ - put_cpu_var(balloon_scratch_page); -} - /* Resets the Xen limit, sets new target, and kicks off processing. */ void balloon_set_new_target(unsigned long target) { _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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