[PATCH] ib_umem_release should decrement mm->pinned_vm from ib_umem_get

From: Shawn Bohrer
Date: Tue Aug 12 2014 - 12:28:42 EST

From: Shawn Bohrer <sbohrer@xxxxxxxxxxxxxxx>

In debugging an application that receives -ENOMEM from ib_reg_mr() I
found that ib_umem_get() can fail because the pinned_vm count has
wrapped causing it to always be larger than the lock limit even with

The wrapping of pinned_vm occurs because the process that calls
ib_reg_mr() will have its mm->pinned_vm count incremented. Later a
different process with a different mm_struct than the one that allocated
the ib_umem struct ends up releasing it which results in decrementing
the new processes mm->pinned_vm count past zero and wrapping.

I'm not entirely sure what circumstances cause a different process to
release the ib_umem than the one that allocated it but the kernel stack
trace of the freeing process from my situation looks like the following:

Call Trace:
[<ffffffff814d64b1>] dump_stack+0x19/0x1b
[<ffffffffa0b522a5>] ib_umem_release+0x1f5/0x200 [ib_core]
[<ffffffffa0b90681>] mlx4_ib_destroy_qp+0x241/0x440 [mlx4_ib]
[<ffffffffa0b4d93c>] ib_destroy_qp+0x12c/0x170 [ib_core]
[<ffffffffa0cc7129>] ib_uverbs_close+0x259/0x4e0 [ib_uverbs]
[<ffffffff81141cba>] __fput+0xba/0x240
[<ffffffff81141e4e>] ____fput+0xe/0x10
[<ffffffff81060894>] task_work_run+0xc4/0xe0
[<ffffffff810029e5>] do_notify_resume+0x95/0xa0
[<ffffffff814e3dd0>] int_signal+0x12/0x17

The following patch fixes the issue by storing the mm_struct of the
process that calls ib_umem_get() so that ib_umem_release and/or
ib_umem_account() can properly decrement the pinned_vm count of the
correct mm_struct.

Signed-off-by: Shawn Bohrer <sbohrer@xxxxxxxxxxxxxxx>
drivers/infiniband/core/umem.c | 17 ++++++++---------
1 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index a3a2e9c..32699024 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -105,6 +105,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr,
umem->length = size;
umem->offset = addr & ~PAGE_MASK;
umem->page_size = PAGE_SIZE;
+ umem->mm = get_task_mm(current);
* We ask for writable memory if any access flags other than
* "remote read" are set. "Local write" and "remote write"
@@ -198,6 +199,7 @@ out:
if (ret < 0) {
if (need_release)
__ib_umem_release(context->device, umem, 0);
+ mmput(umem->mm);
} else
current->mm->pinned_vm = locked;
@@ -229,13 +231,11 @@ static void ib_umem_account(struct work_struct *work)
void ib_umem_release(struct ib_umem *umem)
struct ib_ucontext *context = umem->context;
- struct mm_struct *mm;
unsigned long diff;

__ib_umem_release(umem->context->device, umem, 1);

- mm = get_task_mm(current);
- if (!mm) {
+ if (!umem->mm) {
@@ -251,20 +251,19 @@ void ib_umem_release(struct ib_umem *umem)
* we defer the vm_locked accounting to the system workqueue.
if (context->closing) {
- if (!down_write_trylock(&mm->mmap_sem)) {
+ if (!down_write_trylock(&umem->mm->mmap_sem)) {
INIT_WORK(&umem->work, ib_umem_account);
- umem->mm = mm;
umem->diff = diff;

queue_work(ib_wq, &umem->work);
} else
- down_write(&mm->mmap_sem);
+ down_write(&umem->mm->mmap_sem);

- current->mm->pinned_vm -= diff;
- up_write(&mm->mmap_sem);
- mmput(mm);
+ umem->mm->pinned_vm -= diff;
+ up_write(&umem->mm->mmap_sem);
+ mmput(umem->mm);

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