From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 27 Aug 2007 14:32:21 -0700 (PDT) From: Christoph Lameter Subject: Re: [patch 1/1] alloc_pages(): permit get_zeroed_page(GFP_ATOMIC) from interrupt context In-Reply-To: Message-ID: References: <200708232107.l7NL7XDt026979@imap1.linux-foundation.org> <20070827133347.424f83a6.akpm@linux-foundation.org> <20070827140440.d2109ea5.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Ingo Molnar Cc: linux-mm@kvack.org, thomas.jarosch@intra2net.com, Andrew Morton List-ID: This issue is a result of commit 656dad312fb41ed95ef08325e9df9bece3aacbbb. The intend of moving tests before the check for the highpage was to catch some additional errors. On Mon, 27 Aug 2007, Christoph Lameter wrote: > On Mon, 27 Aug 2007, Andrew Morton wrote: > > > __GFP_HIGHMEM is not set. > > > > : /* > > : * clear_highpage() will use KM_USER0, so it's a bug to use __GFP_ZERO > > : * and __GFP_HIGHMEM from hard or soft interrupt context. > > : */ > > : VM_BUG_ON((gfp_flags & __GFP_HIGHMEM) && in_interrupt()); > > > > __GFP_HIGHMEM is not set > > > > : for (i = 0; i < (1 << order); i++) > > : clear_highpage(page + i); > > > > kmap_atomic() goes boom. > > So the page is not a highmem page. kmap does: > > void *kmap(struct page *page) > { > might_sleep(); > if (!PageHighMem(page)) > return page_address(page); > return kmap_high(page); > } > > -> kmap is fine. > > kmap_atomic() does: > > void *kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot) > { > enum fixed_addresses idx; > unsigned long vaddr; > > /* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */ > pagefault_disable(); > > idx = type + KM_TYPE_NR*smp_processor_id(); > BUG_ON(!pte_none(*(kmap_pte-idx))); > > if (!PageHighMem(page)) > return page_address(page); > > vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx); > set_pte(kmap_pte-idx, mk_pte(page, prot)); > arch_flush_lazy_mmu_mode(); > > return (void*) vaddr; > } > > Move the check for highmem to the beginning of the function? Why > should kmap_atomic fail for a non highmem page? > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org