* Re: 2.5.55-rmk1: user space lossage [not found] <000001c2c287$ffa8eef0$800b040f@bergamot> @ 2003-01-23 9:48 ` David Woodhouse 2003-01-23 9:56 ` Andrew Morton 2003-01-23 10:01 ` David Woodhouse 0 siblings, 2 replies; 5+ messages in thread From: David Woodhouse @ 2003-01-23 9:48 UTC (permalink / raw) To: Christopher Hoover Cc: 'Frank Becker', linux-arm-kernel, 'linux-mtd', akpm, linux-kernel < Snip long thread about init segfaulting immediately at boot on 2.5.55 > ch@murgatroid.com said: > I just dropped jffs2 from 2.5.52 into 2.5.55 and it works, too. ch@murgatroid.com said: > Aha! This is the problem: > - .mmap = generic_file_mmap, > + .mmap = generic_file_readonly_mmap, > If you reverese this change, 2.5.55-rmk1 behaves. Er, yes. generic_file_readonly_mmap() silently removed the VM_MAYWRITE bit from vma->vm_flags when init made a _PRIVATE_ writable mapping, apparently on the basis that we have no writepage(). Then we return success anyway. Then init segfaults when it touches something in that mapping. /me blames akpm. :) -- dwmw2 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: 2.5.55-rmk1: user space lossage 2003-01-23 9:48 ` 2.5.55-rmk1: user space lossage David Woodhouse @ 2003-01-23 9:56 ` Andrew Morton 2003-01-23 10:01 ` David Woodhouse 1 sibling, 0 replies; 5+ messages in thread From: Andrew Morton @ 2003-01-23 9:56 UTC (permalink / raw) To: David Woodhouse; +Cc: ch, fbecker, linux-arm-kernel, linux-mtd, linux-kernel David Woodhouse <dwmw2@infradead.org> wrote: > > /me blames akpm. :) Linus did it! diff -puN mm/filemap.c~generic_file_readonly_mmap-fix mm/filemap.c --- 25/mm/filemap.c~generic_file_readonly_mmap-fix 2003-01-23 01:55:41.000000000 -0800 +++ 25-akpm/mm/filemap.c 2003-01-23 01:55:45.000000000 -0800 @@ -1312,7 +1312,6 @@ int generic_file_readonly_mmap(struct fi { if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) return -EINVAL; - vma->vm_flags &= ~VM_MAYWRITE; return generic_file_mmap(file, vma); } #else _ ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: 2.5.55-rmk1: user space lossage 2003-01-23 9:48 ` 2.5.55-rmk1: user space lossage David Woodhouse 2003-01-23 9:56 ` Andrew Morton @ 2003-01-23 10:01 ` David Woodhouse 2003-01-23 10:06 ` Andrew Morton 1 sibling, 1 reply; 5+ messages in thread From: David Woodhouse @ 2003-01-23 10:01 UTC (permalink / raw) To: Andrew Morton; +Cc: ch, fbecker, linux-arm-kernel, linux-mtd, linux-kernel akpm@digeo.com said: > Linus did it! > diff -puN mm/filemap.c~generic_file_readonly_mmap-fix mm/filemap.c > --- 25/mm/filemap.c~generic_file_readonly_mmap-fix 2003-01-23 01:55:41 -0800 > +++ 25-akpm/mm/filemap.c 2003-01-23 01:55:45 -0800 > @@ -1312,7 +1312,6 @@ int generic_file_readonly_mmap(struct fi > { > if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) > return -EINVAL; > - vma->vm_flags &= ~VM_MAYWRITE; > return generic_file_mmap(file, vma); > } > #else - if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) +- if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) ++ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) ...? -- dwmw2 ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: 2.5.55-rmk1: user space lossage 2003-01-23 10:01 ` David Woodhouse @ 2003-01-23 10:06 ` Andrew Morton 2003-01-23 17:57 ` Hugh Dickins 0 siblings, 1 reply; 5+ messages in thread From: Andrew Morton @ 2003-01-23 10:06 UTC (permalink / raw) To: David Woodhouse; +Cc: ch, fbecker, linux-arm-kernel, linux-mtd, linux-kernel David Woodhouse <dwmw2@infradead.org> wrote: > > > > - if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) > +- if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) > ++ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) Yup. We cannot clear VM_MAYWRITE in there - it turns writeable MAP_PRIVATE mappings into readonly ones. So change it back to the 2.4 form - disallow a writeable MAP_SHARED mapping against filesystems which do no implement ->writepage(). filemap.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff -puN mm/filemap.c~generic_file_readonly_mmap-fix mm/filemap.c --- 25/mm/filemap.c~generic_file_readonly_mmap-fix 2003-01-23 01:55:41.000000000 -0800 +++ 25-akpm/mm/filemap.c 2003-01-23 02:04:05.000000000 -0800 @@ -1308,11 +1308,13 @@ int generic_file_mmap(struct file * file return 0; } +/* + * This is for filesystems which do not implement ->writepage. + */ int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma) { - if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) + if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) return -EINVAL; - vma->vm_flags &= ~VM_MAYWRITE; return generic_file_mmap(file, vma); } #else _ ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: 2.5.55-rmk1: user space lossage 2003-01-23 10:06 ` Andrew Morton @ 2003-01-23 17:57 ` Hugh Dickins 0 siblings, 0 replies; 5+ messages in thread From: Hugh Dickins @ 2003-01-23 17:57 UTC (permalink / raw) To: Andrew Morton; +Cc: David Woodhouse, linux-kernel On Thu, 23 Jan 2003, Andrew Morton wrote: > > We cannot clear VM_MAYWRITE in there - it turns writeable MAP_PRIVATE > mappings into readonly ones. > > So change it back to the 2.4 form - disallow a writeable MAP_SHARED mapping > against filesystems which do no implement ->writepage(). Sorry for late quibbles, but wouldn't patch below be better? Linus did intend that change to the occasionally criticized 2.4 behaviour, this preserves that change while avoiding the bug which hit David. You may notice I've sneaked a ~VM_SHARED in there too. Not because I can say it's necessary, but the VM_MAYWRITE, VM_SHARED treatment is already weird, I'd feel safer if we keep to the same combination as already exists in the !FMODE_WRITE case (see do_mmap_pgoff). Hugh --- 2.5.59-mm2/mm/filemap.c Sat Jan 18 10:37:36 2003 +++ linux/mm/filemap.c Thu Jan 23 16:50:34 2003 @@ -1310,9 +1310,11 @@ int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma) { - if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) - return -EINVAL; - vma->vm_flags &= ~VM_MAYWRITE; + if (vma->vm_flags & VM_SHARED) { + if (vma->vm_flags & VM_WRITE) + return -EINVAL; + vma->vm_flags &= ~(VM_MAYWRITE | VM_SHARED); + } return generic_file_mmap(file, vma); } #else ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2003-01-23 17:46 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2003-01-23 9:48 ` 2.5.55-rmk1: user space lossage David Woodhouse
2003-01-23 9:56 ` Andrew Morton
2003-01-23 10:01 ` David Woodhouse
2003-01-23 10:06 ` Andrew Morton
2003-01-23 17:57 ` Hugh Dickins
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