[PATCH 5/6] kernel: better document the use_mm/unuse_mm API contract
Christoph Hellwig
hch at lst.de
Sat Apr 4 09:41:00 UTC 2020
Switch the function documentation to kerneldoc comments, and add
WARN_ON_ONCE asserts that the calling thread is a kernel thread and
does not have ->mm set (or has ->mm set in the case of unuse_mm).
Also give the functions a kthread_ prefix to better document the
use case.
Signed-off-by: Christoph Hellwig <hch at lst.de>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h | 4 +--
drivers/gpu/drm/i915/gvt/kvmgt.c | 4 +--
drivers/usb/gadget/function/f_fs.c | 4 +--
drivers/usb/gadget/legacy/inode.c | 4 +--
drivers/vhost/vhost.c | 4 +--
fs/io-wq.c | 6 ++--
fs/io_uring.c | 6 ++--
include/linux/kthread.h | 4 +--
kernel/kthread.c | 33 +++++++++++-----------
mm/oom_kill.c | 6 ++--
mm/vmacache.c | 4 +--
11 files changed, 39 insertions(+), 40 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
index bce5e93fefc8..63db84e09408 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h
@@ -192,9 +192,9 @@ uint8_t amdgpu_amdkfd_get_xgmi_hops_count(struct kgd_dev *dst, struct kgd_dev *s
if ((mmptr) == current->mm) { \
valid = !get_user((dst), (wptr)); \
} else if (current->flags & PF_KTHREAD) { \
- use_mm(mmptr); \
+ kthread_use_mm(mmptr); \
valid = !get_user((dst), (wptr)); \
- unuse_mm(mmptr); \
+ kthread_unuse_mm(mmptr); \
} \
pagefault_enable(); \
} \
diff --git a/drivers/gpu/drm/i915/gvt/kvmgt.c b/drivers/gpu/drm/i915/gvt/kvmgt.c
index dee01c371bf5..92e9b340dbc2 100644
--- a/drivers/gpu/drm/i915/gvt/kvmgt.c
+++ b/drivers/gpu/drm/i915/gvt/kvmgt.c
@@ -2048,7 +2048,7 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa,
if (kthread) {
if (!mmget_not_zero(kvm->mm))
return -EFAULT;
- use_mm(kvm->mm);
+ kthread_use_mm(kvm->mm);
}
idx = srcu_read_lock(&kvm->srcu);
@@ -2057,7 +2057,7 @@ static int kvmgt_rw_gpa(unsigned long handle, unsigned long gpa,
srcu_read_unlock(&kvm->srcu, idx);
if (kthread) {
- unuse_mm(kvm->mm);
+ kthread_unuse_mm(kvm->mm);
mmput(kvm->mm);
}
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index c57b1b2507c6..d9e48bd7c692 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -827,9 +827,9 @@ static void ffs_user_copy_worker(struct work_struct *work)
mm_segment_t oldfs = get_fs();
set_fs(USER_DS);
- use_mm(io_data->mm);
+ kthread_use_mm(io_data->mm);
ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
- unuse_mm(io_data->mm);
+ kthread_unuse_mm(io_data->mm);
set_fs(oldfs);
}
diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 8b5233888bf8..a05552bc2ff8 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -462,9 +462,9 @@ static void ep_user_copy_worker(struct work_struct *work)
struct kiocb *iocb = priv->iocb;
size_t ret;
- use_mm(mm);
+ kthread_use_mm(mm);
ret = copy_to_iter(priv->buf, priv->actual, &priv->to);
- unuse_mm(mm);
+ kthread_unuse_mm(mm);
if (!ret)
ret = -EFAULT;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 4e9ce54869af..1787d426a956 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -336,7 +336,7 @@ static int vhost_worker(void *data)
mm_segment_t oldfs = get_fs();
set_fs(USER_DS);
- use_mm(dev->mm);
+ kthread_use_mm(dev->mm);
for (;;) {
/* mb paired w/ kthread_stop */
@@ -364,7 +364,7 @@ static int vhost_worker(void *data)
schedule();
}
}
- unuse_mm(dev->mm);
+ kthread_unuse_mm(dev->mm);
set_fs(oldfs);
return 0;
}
diff --git a/fs/io-wq.c b/fs/io-wq.c
index c49c2bdbafb5..83c2868eff2a 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -169,7 +169,7 @@ static bool __io_worker_unuse(struct io_wqe *wqe, struct io_worker *worker)
}
__set_current_state(TASK_RUNNING);
set_fs(KERNEL_DS);
- unuse_mm(worker->mm);
+ kthread_unuse_mm(worker->mm);
mmput(worker->mm);
worker->mm = NULL;
}
@@ -416,7 +416,7 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe)
static void io_wq_switch_mm(struct io_worker *worker, struct io_wq_work *work)
{
if (worker->mm) {
- unuse_mm(worker->mm);
+ kthread_unuse_mm(worker->mm);
mmput(worker->mm);
worker->mm = NULL;
}
@@ -425,7 +425,7 @@ static void io_wq_switch_mm(struct io_worker *worker, struct io_wq_work *work)
return;
}
if (mmget_not_zero(work->mm)) {
- use_mm(work->mm);
+ kthread_use_mm(work->mm);
if (!worker->mm)
set_fs(USER_DS);
worker->mm = work->mm;
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 27a4ecb724ca..367406381044 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5839,7 +5839,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
err = -EFAULT;
goto fail_req;
}
- use_mm(ctx->sqo_mm);
+ kthread_use_mm(ctx->sqo_mm);
*mm = ctx->sqo_mm;
}
@@ -5911,7 +5911,7 @@ static int io_sq_thread(void *data)
* may sleep.
*/
if (cur_mm) {
- unuse_mm(cur_mm);
+ kthread_unuse_mm(cur_mm);
mmput(cur_mm);
cur_mm = NULL;
}
@@ -5987,7 +5987,7 @@ static int io_sq_thread(void *data)
set_fs(old_fs);
if (cur_mm) {
- unuse_mm(cur_mm);
+ kthread_unuse_mm(cur_mm);
mmput(cur_mm);
}
revert_creds(old_cred);
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index c2d40c9672d6..12258ea077cf 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -200,8 +200,8 @@ bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *work);
void kthread_destroy_worker(struct kthread_worker *worker);
-void use_mm(struct mm_struct *mm);
-void unuse_mm(struct mm_struct *mm);
+void kthread_use_mm(struct mm_struct *mm);
+void kthread_unuse_mm(struct mm_struct *mm);
struct cgroup_subsys_state;
diff --git a/kernel/kthread.c b/kernel/kthread.c
index ce4610316377..316db17f6b4f 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1208,18 +1208,18 @@ void kthread_destroy_worker(struct kthread_worker *worker)
}
EXPORT_SYMBOL(kthread_destroy_worker);
-/*
- * use_mm
- * Makes the calling kernel thread take on the specified
- * mm context.
- * (Note: this routine is intended to be called only
- * from a kernel thread context)
+/**
+ * kthread_use_mm - make the calling kthread operate on an address space
+ * @mm: address space to operate on
*/
-void use_mm(struct mm_struct *mm)
+void kthread_use_mm(struct mm_struct *mm)
{
struct mm_struct *active_mm;
struct task_struct *tsk = current;
+ WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
+ WARN_ON_ONCE(tsk->mm);
+
task_lock(tsk);
active_mm = tsk->active_mm;
if (active_mm != mm) {
@@ -1236,20 +1236,19 @@ void use_mm(struct mm_struct *mm)
if (active_mm != mm)
mmdrop(active_mm);
}
-EXPORT_SYMBOL_GPL(use_mm);
+EXPORT_SYMBOL_GPL(kthread_use_mm);
-/*
- * unuse_mm
- * Reverses the effect of use_mm, i.e. releases the
- * specified mm context which was earlier taken on
- * by the calling kernel thread
- * (Note: this routine is intended to be called only
- * from a kernel thread context)
+/**
+ * kthread_use_mm - reverse the effect of kthread_use_mm()
+ * @mm: address space to operate on
*/
-void unuse_mm(struct mm_struct *mm)
+void kthread_unuse_mm(struct mm_struct *mm)
{
struct task_struct *tsk = current;
+ WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
+ WARN_ON_ONCE(!tsk->mm);
+
task_lock(tsk);
sync_mm_rss(mm);
tsk->mm = NULL;
@@ -1257,7 +1256,7 @@ void unuse_mm(struct mm_struct *mm)
enter_lazy_tlb(mm, tsk);
task_unlock(tsk);
}
-EXPORT_SYMBOL_GPL(unuse_mm);
+EXPORT_SYMBOL_GPL(kthread_unuse_mm);
#ifdef CONFIG_BLK_CGROUP
/**
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index dfc357614e56..958d2972313f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -126,7 +126,7 @@ static bool oom_cpuset_eligible(struct task_struct *tsk, struct oom_control *oc)
/*
* The process p may have detached its own ->mm while exiting or through
- * use_mm(), but one or more of its subthreads may still have a valid
+ * kthread_use_mm(), but one or more of its subthreads may still have a valid
* pointer. Return p, or any of its subthreads with a valid ->mm, with
* task_lock() held.
*/
@@ -919,8 +919,8 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
continue;
}
/*
- * No use_mm() user needs to read from the userspace so we are
- * ok to reap it.
+ * No kthead_use_mm() user needs to read from the userspace so
+ * we are ok to reap it.
*/
if (unlikely(p->flags & PF_KTHREAD))
continue;
diff --git a/mm/vmacache.c b/mm/vmacache.c
index cdc32a3b02fa..ceedbab82106 100644
--- a/mm/vmacache.c
+++ b/mm/vmacache.c
@@ -25,8 +25,8 @@
* task's vmacache pertains to a different mm (ie, its own). There is
* nothing we can do here.
*
- * Also handle the case where a kernel thread has adopted this mm via use_mm().
- * That kernel thread's vmacache is not applicable to this mm.
+ * Also handle the case where a kernel thread has adopted this mm via
+ * kthread_use_mm(). That kernel thread's vmacache is not applicable to this mm.
*/
static inline bool vmacache_valid_mm(struct mm_struct *mm)
{
--
2.25.1
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