mlx5_ib_update_xlt() must be protected against parallel free of the MR it
is accessing, also it must be called single threaded while updating the
HW. Otherwise we can have races of the form:
CPU0 CPU1
mlx5_ib_update_xlt()
mlx5_odp_populate_klm()
odp_lookup() == NULL
pklm = ZAP
implicit_mr_get_data()
implicit_mr_alloc()
<update interval tree>
mlx5_ib_update_xlt
mlx5_odp_populate_klm()
odp_lookup() != NULL
pklm = VALID
mlx5_ib_post_send_wait()
mlx5_ib_post_send_wait() // Replaces VALID with ZAP
This can be solved by putting both the SRCU and the umem_mutex lock around
every call to mlx5_ib_update_xlt(). This ensures that the content of the
interval tree relavent to mlx5_odp_populate_klm() (ie mr->parent == mr)
will not change while it is running, and thus the posted WRs to update the
KLM will always reflect the correct information.
The race above will resolve by either having CPU1 wait till CPU0 completes
the ZAP or CPU0 will run after the add and instead store VALID.
The pagefault path adding children already holds the umem_mutex and SRCU,
so the only missed lock is during MR destruction.
Fixes: 81713d3788 ("IB/mlx5: Add implicit MR support")
Link: https://lore.kernel.org/r/20191001153821.23621-3-jgg@ziepe.ca
Reviewed-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
f28b1932ea