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

[Shawn Bohrer <shawn.bohrer@gmail.com>]

From: Shawn Bohrer <sbohrer@rgmadvisors.com>

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
RLIMIT_MEMLOCK set to RLIM_INFINITY.

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@rgmadvisors.com>
---
 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);
 		kfree(umem);
 	} 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) {
 		kfree(umem);
 		return;
 	}
@@ -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);
 			return;
 		}
 	} 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);
 	kfree(umem);
 }
 EXPORT_SYMBOL(ib_umem_release);
-- 
1.7.7.6