From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 27 Aug 2007 14:20:57 -0700 (PDT) From: Christoph Lameter Subject: Re: [patch 1/1] alloc_pages(): permit get_zeroed_page(GFP_ATOMIC) from interrupt context In-Reply-To: <20070827140440.d2109ea5.akpm@linux-foundation.org> 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: Andrew Morton Cc: linux-mm@kvack.org, thomas.jarosch@intra2net.com List-ID: 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