From ef1b51f7735e0988ea6bf99fd6eec4698e965b91 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Thu, 4 Jun 2020 16:48:28 -0700 Subject: [PATCH] powerpc/pseries/hotplug-memory: stop checking is_mem_section_removable() In commit 53cdc1cb29e8 ("drivers/base/memory.c: indicate all memory blocks as removable"), the user space interface to compute whether a memory block can be offlined (exposed via /sys/devices/system/memory/memoryX/removable) has effectively been deprecated. We want to remove the leftovers of the kernel implementation. When offlining a memory block (mm/memory_hotplug.c:__offline_pages()), we'll start by: 1. Testing if it contains any holes, and reject if so 2. Testing if pages belong to different zones, and reject if so 3. Isolating the page range, checking if it contains any unmovable pages Using is_mem_section_removable() before trying to offline is not only racy, it can easily result in false positives/negatives. Let's stop manually checking is_mem_section_removable(), and let device_offline() handle it completely instead. We can remove the racy is_mem_section_removable() implementation next. We now take more locks (e.g., memory hotplug lock when offlining and the zone lock when isolating), but maybe we should optimize that implementation instead if this ever becomes a real problem (after all, memory unplug is already an expensive operation). We started using is_mem_section_removable() in commit 51925fb3c5c9 ("powerpc/pseries: Implement memory hotplug remove in the kernel"), with the initial hotremove support of lmbs. Signed-off-by: David Hildenbrand Signed-off-by: Andrew Morton Cc: Nathan Fontenot Cc: Michael Ellerman Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Michal Hocko Cc: Oscar Salvador Cc: Baoquan He Cc: Wei Yang Link: http://lkml.kernel.org/r/20200407135416.24093-2-david@redhat.com Signed-off-by: Linus Torvalds --- arch/powerpc/platforms/pseries/hotplug-memory.c | 26 +++---------------------- 1 file changed, 3 insertions(+), 23 deletions(-) diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c index b2cde17..5ace2f9 100644 --- a/arch/powerpc/platforms/pseries/hotplug-memory.c +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c @@ -337,39 +337,19 @@ static int pseries_remove_mem_node(struct device_node *np) static bool lmb_is_removable(struct drmem_lmb *lmb) { - int i, scns_per_block; - bool rc = true; - unsigned long pfn, block_sz; - u64 phys_addr; - if (!(lmb->flags & DRCONF_MEM_ASSIGNED)) return false; - block_sz = memory_block_size_bytes(); - scns_per_block = block_sz / MIN_MEMORY_BLOCK_SIZE; - phys_addr = lmb->base_addr; - #ifdef CONFIG_FA_DUMP /* * Don't hot-remove memory that falls in fadump boot memory area * and memory that is reserved for capturing old kernel memory. */ - if (is_fadump_memory_area(phys_addr, block_sz)) + if (is_fadump_memory_area(lmb->base_addr, memory_block_size_bytes())) return false; #endif - - for (i = 0; i < scns_per_block; i++) { - pfn = PFN_DOWN(phys_addr); - if (!pfn_in_present_section(pfn)) { - phys_addr += MIN_MEMORY_BLOCK_SIZE; - continue; - } - - rc = rc && is_mem_section_removable(pfn, PAGES_PER_SECTION); - phys_addr += MIN_MEMORY_BLOCK_SIZE; - } - - return rc; + /* device_offline() will determine if we can actually remove this lmb */ + return true; } static int dlpar_add_lmb(struct drmem_lmb *); -- 2.7.4