Messages in this thread | | | Date | Tue, 24 Apr 2018 23:28:59 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCH net-next 1/2] tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive |
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On Tue, Apr 24, 2018 at 10:27:21PM -0700, Eric Dumazet wrote: > When adding tcp mmap() implementation, I forgot that socket lock > had to be taken before current->mm->mmap_sem. syzbot eventually caught > the bug. > > Since we can not lock the socket in tcp mmap() handler we have to > split the operation in two phases. > > 1) mmap() on a tcp socket simply reserves VMA space, and nothing else. > This operation does not involve any TCP locking. > > 2) setsockopt(fd, IPPROTO_TCP, TCP_ZEROCOPY_RECEIVE, ...) implements > the transfert of pages from skbs to one VMA. > This operation only uses down_read(¤t->mm->mmap_sem) after > holding TCP lock, thus solving the lockdep issue. > > This new implementation was suggested by Andy Lutomirski with great details.
Thanks, this looks much more sensible to me.
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