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H A D | mmap.c | diff 33bfad54b58cf05cfe6678c3ec9235d4bc8db4c2 Fri Jan 30 20:37:22 CET 2009 Linus Torvalds <torvalds@linux-foundation.org> Allow opportunistic merging of VM_CAN_NONLINEAR areas
Commit de33c8db5910cda599899dd431cc30d7c1018cbf ("Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments") unified the vma merging of anonymous and file maps to just one place, which simplified the code and fixed a use-after-free bug that could cause an oops.
But by doing the merge opportunistically before even having called ->mmap() on the file method, it now compares two different 'vm_flags' values: the pre-mmap() value of the new not-yet-formed vma, and previous mappings of the same file around it.
And in doing so, it refused to merge the common file case, which adds a marker to say "I can be made non-linear".
This fixes it by just adding a set of flags that don't have to match, because we know they are ok to merge. Currently it's only that single VM_CAN_NONLINEAR flag, but at least conceptually there could be others in the future.
Reported-and-acked-by: Hugh Dickins <hugh@veritas.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Greg KH <gregkh@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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