From: Jianxing Wang wangjianxing@loongson.cn

mainline inclusion from mainline-v5.19-rc1 commit b191c9bc334a936775843867485c207e23b30e1b category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I9N6YV CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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free a large list of pages maybe cause rcu_sched starved on non-preemptible kernels. howerver free_unref_page_list maybe can't cond_resched as it maybe called in interrupt or atomic context, especially can't detect atomic context in CONFIG_PREEMPTION=n.

The issue is detected in guest with kvm cpu 200% overcommit, however I didn't see the warning in the host with the same application. I'm sure that the patch is needed for guest kernel, but no sure for host.

To reproduce, set up two virtual machines in one host machine, per vm has the same number cpu and half memory of host. the run ltpstress.sh in per vm, then will see rcu stall warning.kernel is preempt disabled, append kernel command 'preempt=none' if enable dynamic preempt . It could detected in loongson machine(32 core, 128G mem) and ProLiant DL380 Gen9(x86 E5-2680, 28 core, 64G mem)

tlb flush batch count depends on PAGE_SIZE, it's too large if PAGE_SIZE > 4K, here limit free batch count with 512. And add schedule point in tlb_batch_pages_flush.

rcu: rcu_sched kthread starved for 5359 jiffies! g454793 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=19 [...] Call Trace: free_unref_page_list+0x19c/0x270 release_pages+0x3cc/0x498 tlb_flush_mmu_free+0x44/0x70 zap_pte_range+0x450/0x738 unmap_page_range+0x108/0x240 unmap_vmas+0x74/0xf0 unmap_region+0xb0/0x120 do_munmap+0x264/0x438 vm_munmap+0x58/0xa0 sys_munmap+0x10/0x20 syscall_common+0x24/0x38

Link: https://lkml.kernel.org/r/20220317072857.2635262-1-wangjianxing@loongson.cn Signed-off-by: Jianxing Wang wangjianxing@loongson.cn Signed-off-by: Peter Zijlstra peterz@infradead.org Cc: Will Deacon will@kernel.org Cc: Nicholas Piggin npiggin@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Jinjiang Tu tujinjiang@huawei.com --- mm/mmu_gather.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c index 205fdbb5792a..1c66771f088b 100644 --- a/mm/mmu_gather.c +++ b/mm/mmu_gather.c @@ -46,8 +46,20 @@ static void tlb_batch_pages_flush(struct mmu_gather *tlb) struct mmu_gather_batch *batch;

for (batch = &tlb->local; batch && batch->nr; batch = batch->next) { - free_pages_and_swap_cache(batch->pages, batch->nr); - batch->nr = 0; + struct page **pages = batch->pages; + + do { + /* + * limit free batch count when PAGE_SIZE > 4K + */ + unsigned int nr = min(512U, batch->nr); + + free_pages_and_swap_cache(pages, nr); + pages += nr; + batch->nr -= nr; + + cond_resched(); + } while (batch->nr); } tlb->active = &tlb->local; }