Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751862AbZIYEjV (ORCPT ); Fri, 25 Sep 2009 00:39:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751403AbZIYEjS (ORCPT ); Fri, 25 Sep 2009 00:39:18 -0400 Received: from mail-iw0-f178.google.com ([209.85.223.178]:35551 "EHLO mail-iw0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751241AbZIYEjS convert rfc822-to-8bit (ORCPT ); Fri, 25 Sep 2009 00:39:18 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=owJ4QsFHkspE9kGvjECOBsiaxp5uphMhMxakMrwobrU/hN/3fdtv+SIxY9zhn413QY UF8cAEnEmYAlYTEdCV5YspL24lEQbzd5ur5ipjtMfFJflQ+nXOBn5mbeYnQtqk9v7JkF LM0ZWo86h3Dm0/ssFGG2x6+dsC4GhRDxCL8Ps= MIME-Version: 1.0 In-Reply-To: <20090924141310.19746.31678.stgit@warthog.procyon.org.uk> References: <20090924141310.19746.31678.stgit@warthog.procyon.org.uk> Date: Fri, 25 Sep 2009 12:39:21 +0800 Message-ID: <7d86d44a0909242139v32a0ef6bh68386cbda31d0682@mail.gmail.com> Subject: Re: [PATCH] NOMMU: Fix MAP_PRIVATE mmap() of objects where the data can be mapped directly From: graff yang To: David Howells Cc: torvalds@osdl.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Pekka Enberg , Paul Mundt , Mel Gorman , Greg Ungerer Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7160 Lines: 158 On Thu, Sep 24, 2009 at 10:13 PM, David Howells wrote: > Fix MAP_PRIVATE mmap() of files and devices where the data in the backing store > might be mapped directly. Use the BDI_CAP_MAP_DIRECT capability flag to govern > whether or not we should be trying to map a file directly. This can be used to > determine whether or not a region has been filled in at the point where we call > do_mmap_shared() or do_mmap_private(). > > The BDI_CAP_MAP_DIRECT capability flag is cleared by validate_mmap_request() if > there's any reason we can't use it. It's also cleared in do_mmap_pgoff() if > f_op->get_unmapped_area() fails. > > > Without this fix, attempting to run a program from a RomFS image on a > non-mappable MTD partition results in a BUG as the kernel attempts XIP, and > this can be caught in gdb: > > Program received signal SIGABRT, Aborted. > 0xc005dce8 in add_nommu_region (region=) at mm/nommu.c:547 > (gdb) bt > #0 0xc005dce8 in add_nommu_region (region=) at mm/nommu.c:547 > #1 0xc005f168 in do_mmap_pgoff (file=0xc31a6620, addr=, len=3808, prot=3, flags=6146, pgoff=0) at mm/nommu.c:1373 > #2 0xc00a96b8 in elf_fdpic_map_file (params=0xc33fbbec, file=0xc31a6620, mm=0xc31bef60, what=0xc0213144 "executable") at mm.h:1145 > #3 0xc00aa8b4 in load_elf_fdpic_binary (bprm=0xc316cb00, regs=) at fs/binfmt_elf_fdpic.c:343 > #4 0xc006b588 in search_binary_handler (bprm=0x6, regs=0xc33fbce0) at fs/exec.c:1234 > #5 0xc006c648 in do_execve (filename=, argv=0xc3ad14cc, envp=0xc3ad1460, regs=0xc33fbce0) at fs/exec.c:1356 > #6 0xc0008cf0 in sys_execve (name=, argv=0xc3ad14cc, envp=0xc3ad1460) at arch/frv/kernel/process.c:263 > #7 0xc00075dc in __syscall_call () at arch/frv/kernel/entry.S:897 > > > Note that this fix does the following commit differently: > > commit a190887b58c32d19c2eee007c5eb8faa970a69ba > Author: David Howells > Date: Sat Sep 5 11:17:07 2009 -0700 > nommu: fix error handling in do_mmap_pgoff() > > Reported-by: Graff Yang > Signed-off-by: David Howells > Cc: Pekka Enberg > Cc: Paul Mundt > Cc: Mel Gorman > Cc: Greg Ungerer > --- > > mm/nommu.c | 34 ++++++++++++---------------------- > 1 files changed, 12 insertions(+), 22 deletions(-) > > > diff --git a/mm/nommu.c b/mm/nommu.c > index c459aec..cc24d9f 100644 > --- a/mm/nommu.c > +++ b/mm/nommu.c > @@ -1074,7 +1074,7 @@ static int do_mmap_shared_file(struct vm_area_struct *vma) > ret = vma->vm_file->f_op->mmap(vma->vm_file, vma); > if (ret == 0) { > vma->vm_region->vm_top = vma->vm_region->vm_end; > - return ret; > + return 0; > } > if (ret != -ENOSYS) > return ret; > @@ -1091,7 +1091,8 @@ static int do_mmap_shared_file(struct vm_area_struct *vma) > */ > static int do_mmap_private(struct vm_area_struct *vma, > struct vm_region *region, > - unsigned long len) > + unsigned long len, > + unsigned long capabilities) > { > struct page *pages; > unsigned long total, point, n, rlen; > @@ -1102,13 +1103,13 @@ static int do_mmap_private(struct vm_area_struct *vma, > * shared mappings on devices or memory > * - VM_MAYSHARE will be set if it may attempt to share > */ > - if (vma->vm_file) { > + if (capabilities & BDI_CAP_MAP_DIRECT) { This will breaks many drivers, e.g. some frame-buffer drivers, on NOMMU system. Because they don't have get_unmapped_area(). These drivers depend on it's mmap() to return the frame-buffer base address. -Graff > ret = vma->vm_file->f_op->mmap(vma->vm_file, vma); > if (ret == 0) { > /* shouldn't return success if we're not sharing */ > BUG_ON(!(vma->vm_flags & VM_MAYSHARE)); > vma->vm_region->vm_top = vma->vm_region->vm_end; > - return ret; > + return 0; > } > if (ret != -ENOSYS) > return ret; > @@ -1346,7 +1347,7 @@ unsigned long do_mmap_pgoff(struct file *file, > * - this is the hook for quasi-memory character devices to > * tell us the location of a shared mapping > */ > - if (file && file->f_op->get_unmapped_area) { > + if (capabilities & BDI_CAP_MAP_DIRECT) { > addr = file->f_op->get_unmapped_area(file, addr, len, > pgoff, flags); > if (IS_ERR((void *) addr)) { > @@ -1370,15 +1371,17 @@ unsigned long do_mmap_pgoff(struct file *file, > } > > vma->vm_region = region; > - add_nommu_region(region); > > - /* set up the mapping */ > + /* set up the mapping > + * - the region is filled in if BDI_CAP_MAP_DIRECT is still set > + */ > if (file && vma->vm_flags & VM_SHARED) > ret = do_mmap_shared_file(vma); > else > - ret = do_mmap_private(vma, region, len); > + ret = do_mmap_private(vma, region, len, capabilities); > if (ret < 0) > - goto error_put_region; > + goto error_just_free; > + add_nommu_region(region); > > /* okay... we have a mapping; now we have to register it */ > result = vma->vm_start; > @@ -1396,19 +1399,6 @@ share: > kleave(" = %lx", result); > return result; > > -error_put_region: > - __put_nommu_region(region); > - if (vma) { > - if (vma->vm_file) { > - fput(vma->vm_file); > - if (vma->vm_flags & VM_EXECUTABLE) > - removed_exe_file_vma(vma->vm_mm); > - } > - kmem_cache_free(vm_area_cachep, vma); > - } > - kleave(" = %d [pr]", ret); > - return ret; > - > error_just_free: > up_write(&nommu_region_sem); > error: > > -- -Graff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/