The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a4e63bce1414df7ab6eb82ca9feb8494ce13e554 Mon Sep 17 00:00:00 2001

From: Jason Gunthorpe jgg@ziepe.ca Date: Thu, 27 Feb 2020 13:41:18 +0200 Subject: [PATCH] RDMA/odp: Ensure the mm is still alive before creating an implicit child

Registration of a mmu_notifier requires the caller to hold a mmget() on the mm as registration is not permitted to race with exit_mmap(). There is a BUG_ON inside the mmu_notifier to guard against this.

Normally creating a umem is done against current which implicitly holds the mmget(), however an implicit ODP child is created from a pagefault work queue and is not guaranteed to have a mmget().

Call mmget() around this registration and abort faulting if the MM has gone to exit_mmap().

Before the patch below the notifier was registered when the implicit ODP parent was created, so there was no chance to register a notifier outside of current.

Fixes: c571feca2dc9 ("RDMA/odp: use mmu_notifier_get/put for 'struct ib_ucontext_per_mm'") Link: https://lore.kernel.org/r/20200227114118.94736-1-leon@kernel.org Signed-off-by: Leon Romanovsky leonro@mellanox.com Signed-off-by: Jason Gunthorpe jgg@mellanox.com

diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c index b8c657b28380..cd656ad4953b 100644 --- a/drivers/infiniband/core/umem_odp.c +++ b/drivers/infiniband/core/umem_odp.c @@ -181,14 +181,28 @@ ib_umem_odp_alloc_child(struct ib_umem_odp *root, unsigned long addr, odp_data->page_shift = PAGE_SHIFT; odp_data->notifier.ops = ops;

+ /* + * A mmget must be held when registering a notifier, the owming_mm only + * has a mm_grab at this point. + */ + if (!mmget_not_zero(umem->owning_mm)) { + ret = -EFAULT; + goto out_free; + } + odp_data->tgid = get_pid(root->tgid); ret = ib_init_umem_odp(odp_data, ops); - if (ret) { - put_pid(odp_data->tgid); - kfree(odp_data); - return ERR_PTR(ret); - } + if (ret) + goto out_tgid; + mmput(umem->owning_mm); return odp_data; + +out_tgid: + put_pid(odp_data->tgid); + mmput(umem->owning_mm); +out_free: + kfree(odp_data); + return ERR_PTR(ret); } EXPORT_SYMBOL(ib_umem_odp_alloc_child);