uprobes: __replace_page() should not use page_address_in_vma()
authorOleg Nesterov <oleg@redhat.com>
Sun, 29 Jul 2012 18:22:16 +0000 (20:22 +0200)
committerIngo Molnar <mingo@kernel.org>
Mon, 30 Jul 2012 09:27:19 +0000 (11:27 +0200)
commitc517ee744b96e441d9c731e245f83c6d08dc0a19
tree8d7f7b86767ba2d5c62c2d421f388949f0483c85
parentf403072c6108e15f319a4a5036b650c77760522c
uprobes: __replace_page() should not use page_address_in_vma()

page_address_in_vma(old_page) in __replace_page() is ugly and
wrong. The caller already knows the correct virtual address,
this page was found by get_user_pages(vaddr).

However, page_address_in_vma() can actually fail if
page->mapping was cleared by __delete_from_page_cache() after
get_user_pages() returns. But this means the race with page
reclaim, write_opcode() should not fail, it should retry and
read this page again. Probably the race with remove_mapping() is
not possible due to page_freeze_refs() logic, but afaics at
least shmem_writepage()->shmem_delete_from_page_cache() can
clear ->mapping.

We could change __replace_page() to return -EAGAIN in this case,
but it would be better to simply use the caller's vaddr and rely
on page_check_address().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar.vnet.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20120729182216.GA20311@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
kernel/events/uprobes.c