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authorHugh Dickins <hugh@veritas.com>2009-01-06 14:39:32 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-06 15:59:03 -0800
commit878b63ac889df706d01048f2c110e322ad2f996d (patch)
treee0bd69b890fda939fc190675d977dd0fd75e0427 /firmware
parent2da02997e08d3efe8174c7a47696e6f7cbe69ba9 (diff)
mm: gup persist for write permission
do_wp_page()'s VM_FAULT_WRITE return value tells __get_user_pages() that COW has been done if necessary, though it may be leaving the pte without write permission - for the odd case of forced writing to a readonly vma for ptrace. At present GUP then retries the follow_page() without asking for write permission, to escape an endless loop when forced. But an application may be relying on GUP to guarantee a writable page which won't be COWed again when written from userspace, whereas a race here might leave a readonly pte in place? Change the VM_FAULT_WRITE handling to ask follow_page() for write permission again, except in that odd case of forced writing to a readonly vma. Signed-off-by: Hugh Dickins <hugh@veritas.com> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com> Cc: Rik van Riel <riel@redhat.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Robin Holt <holt@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'firmware')
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