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authorOleg Nesterov <oleg@redhat.com>2009-07-09 17:28:49 -0400
committerJames Morris <jmorris@namei.org>2009-07-16 19:11:31 -0400
commit967cc5371113f9806b39a2ebb2174af2883d96fe (patch)
treed99845169cde5e238a02d1e984ff9aa65b66482f /fs/ocfs2/ioctl.h
parent5bb459bb45d1ad3c177485dcf0af01580aa31125 (diff)
kernel: is_current_single_threaded: don't use ->mmap_sem
is_current_single_threaded() can safely miss a freshly forked CLONE_VM task, but in this case it must not miss its parent. That is why we take mm->mmap_sem for writing to make sure a thread/task with the same ->mm can't pass exit_mm() and disappear. However we can avoid ->mmap_sem and rely on rcu/barriers: - if we do not see the exiting parent on thread/process list we see the result of list_del_rcu(), in this case we must also see the result of list_add_rcu() which does wmb(). - if we do see the parent but its ->mm == NULL, we need rmb() to make sure we can't miss the child. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: James Morris <jmorris@namei.org>
Diffstat (limited to 'fs/ocfs2/ioctl.h')
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