On 18 Feb 2020, at 14:13, zerons <sironhide0null@xxxxxxxxx> wrote:
Hi, all
In net/rds/rdma.c
(https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/net/rds/rdma.c?h=v5.5.3*n419__;Iw!!GqivPVa7Brio!OwwQCLtjDsKmhaIz0sfaOVSuC4ai5t5_FgB7yqNExGOCBtACtIGLF61NNJyqSDtIAcGoPg$ ),
there may be a race condition between rds_rdma_unuse() and rds_free_mr().
Hmmm.. I didn't see email before in my inbox. Please post
questions/patches on netdev in future which is the correct mailing list.
It seems that this one need some specific devices to run test,
unfortunately, I don't have any of these.
I've already sent two emails to the maintainer for help, no response yet,
(the email address may not be in use).
0) in rds_recv_incoming_exthdrs(), it calls rds_rdma_unuse() when receive an
extension header with force=0, if the victim mr does not have RDS_RDMA_USE_ONCE
flag set, then the mr would stay in the rbtree. Without any lock, it tries to
call mr->r_trans->sync_mr().
1) in rds_free_mr(), the same mr is found, and then freed. The mr->r_refcount
doesn't change while rds_mr_tree_walk().
0) back in rds_rdma_unuse(), the victim mr get used again, call
mr->r_trans->sync_mr().
Could this race condition actually happen?
force=0 is an interesting scenario. Let me think about it and get back.
Thanks for report.
Regards,
Santosh
