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Message-ID: <CACT4Y+aKOC83Dm=wwZT9zsxi+MAxwZnHp1wBLbF6VH9YPAWLCw@mail.gmail.com>
Date: Tue, 17 Dec 2019 14:03:28 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Alan Stern <stern@...land.harvard.edu>,
Jiri Kosina <jikos@...nel.org>,
Benjamin Tissoires <benjamin.tissoires@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
USB list <linux-usb@...r.kernel.org>,
"open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Alexander Potapenko <glider@...gle.com>,
Marco Elver <elver@...gle.com>
Subject: Re: [PATCH RFC 1/2] kcov: collect coverage from interrupts
On Thu, Dec 12, 2019 at 6:15 PM Andrey Konovalov <andreyknvl@...gle.com> wrote:
>
> This change extends kcov remote coverage support to allow collecting
> coverage from interrupts in addition to kernel background threads.
>
> To collect coverage from code that is executed in interrupt context, a
> part of that code has to be annotated with kcov_remote_start/stop() in a
> similar way as how it is done for global kernel background threads. Then
> the handle used for the annotations has to be passed to the
> KCOV_REMOTE_ENABLE ioctl.
>
> Internally this patch adjusts the __sanitizer_cov_trace_pc() compiler
> inserted callback to not bail out when called from interrupt context.
> kcov_remote_start/stop() are updated to save/restore the current per
> task kcov state in a per-cpu area (in case the interrupt came when the
> kernel was already collecting coverage in task context). Coverage from
> interrupts is collected into pre-allocated per-cpu areas, whose size is
> controlled by the new CONFIG_KCOV_IRQ_AREA_SIZE.
>
> This patch also cleans up some of kcov debug messages.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
> Documentation/dev-tools/kcov.rst | 16 +--
> drivers/usb/gadget/udc/dummy_hcd.c | 1 +
> include/linux/sched.h | 3 +
> kernel/kcov.c | 196 +++++++++++++++++++----------
> lib/Kconfig.debug | 9 ++
> 5 files changed, 154 insertions(+), 71 deletions(-)
>
> diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst
> index 1c4e1825d769..fc2bc6883431 100644
> --- a/Documentation/dev-tools/kcov.rst
> +++ b/Documentation/dev-tools/kcov.rst
> @@ -217,14 +217,14 @@ This allows to collect coverage from two types of kernel background
> threads: the global ones, that are spawned during kernel boot in a limited
> number of instances (e.g. one USB hub_event() worker thread is spawned per
> USB HCD); and the local ones, that are spawned when a user interacts with
> -some kernel interface (e.g. vhost workers).
> +some kernel interface (e.g. vhost workers); as well as from interrupts.
>
> -To enable collecting coverage from a global background thread, a unique
> -global handle must be assigned and passed to the corresponding
> -kcov_remote_start() call. Then a userspace process can pass a list of such
> -handles to the KCOV_REMOTE_ENABLE ioctl in the handles array field of the
> -kcov_remote_arg struct. This will attach the used kcov device to the code
> -sections, that are referenced by those handles.
> +To enable collecting coverage from a global background thread or from an
> +interrupt, a unique global handle must be assigned and passed to the
> +corresponding kcov_remote_start() call. Then a userspace process can pass
> +a list of such handles to the KCOV_REMOTE_ENABLE ioctl in the handles
> +array field of the kcov_remote_arg struct. This will attach the used kcov
> +device to the code sections, that are referenced by those handles.
>
> Since there might be many local background threads spawned from different
> userspace processes, we can't use a single global handle per annotation.
> @@ -242,7 +242,7 @@ handles as they don't belong to a particular subsystem. The bytes 4-7 are
> currently reserved and must be zero. In the future the number of bytes
> used for the subsystem or handle ids might be increased.
>
> -When a particular userspace proccess collects coverage by via a common
> +When a particular userspace proccess collects coverage via a common
> handle, kcov will collect coverage for each code section that is annotated
> to use the common handle obtained as kcov_handle from the current
> task_struct. However non common handles allow to collect coverage
> diff --git a/drivers/usb/gadget/udc/dummy_hcd.c b/drivers/usb/gadget/udc/dummy_hcd.c
> index 4c9d1e49d5ed..faf84ada71a5 100644
> --- a/drivers/usb/gadget/udc/dummy_hcd.c
> +++ b/drivers/usb/gadget/udc/dummy_hcd.c
> @@ -38,6 +38,7 @@
> #include <linux/usb/gadget.h>
> #include <linux/usb/hcd.h>
> #include <linux/scatterlist.h>
> +#include <linux/kcov.h>
>
> #include <asm/byteorder.h>
> #include <linux/io.h>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 467d26046416..47d1d556f795 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1229,6 +1229,9 @@ struct task_struct {
>
> /* KCOV sequence number: */
> int kcov_sequence;
> +
> + /* Collect coverage from interrupt context: */
> + bool kcov_interrupt;
> #endif
>
> #ifdef CONFIG_MEMCG
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index f50354202dbe..5b48a7a5c465 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -26,6 +26,7 @@
> #include <asm/setup.h>
>
> #define kcov_debug(fmt, ...) pr_debug("%s: " fmt, __func__, ##__VA_ARGS__)
> +#define kcov_err(fmt, ...) pr_err("%s: " fmt, __func__, ##__VA_ARGS__)
>
> /* Number of 64-bit words written per one comparison: */
> #define KCOV_WORDS_PER_CMP 4
> @@ -86,6 +87,17 @@ static DEFINE_SPINLOCK(kcov_remote_lock);
> static DEFINE_HASHTABLE(kcov_remote_map, 4);
> static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);
>
> +struct kcov_remote_irq_data {
> + unsigned int mode;
> + unsigned int size;
> + void *area;
> + struct kcov *kcov;
> + unsigned long flags;
> +};
> +
> +DEFINE_PER_CPU(struct kcov_remote_irq_data, kcov_remote_irq);
> +DEFINE_PER_CPU(void *, kcov_irq_area);
> +
> /* Must be called with kcov_remote_lock locked. */
> static struct kcov_remote *kcov_remote_find(u64 handle)
> {
> @@ -98,6 +110,7 @@ static struct kcov_remote *kcov_remote_find(u64 handle)
> return NULL;
> }
>
> +/* Must be called with kcov_remote_lock locked. */
> static struct kcov_remote *kcov_remote_add(struct kcov *kcov, u64 handle)
> {
> struct kcov_remote *remote;
> @@ -119,16 +132,13 @@ static struct kcov_remote_area *kcov_remote_area_get(unsigned int size)
> struct kcov_remote_area *area;
> struct list_head *pos;
>
> - kcov_debug("size = %u\n", size);
> list_for_each(pos, &kcov_remote_areas) {
> area = list_entry(pos, struct kcov_remote_area, list);
> if (area->size == size) {
> list_del(&area->list);
> - kcov_debug("rv = %px\n", area);
> return area;
> }
> }
> - kcov_debug("rv = NULL\n");
> return NULL;
> }
>
> @@ -136,7 +146,6 @@ static struct kcov_remote_area *kcov_remote_area_get(unsigned int size)
> static void kcov_remote_area_put(struct kcov_remote_area *area,
> unsigned int size)
> {
> - kcov_debug("area = %px, size = %u\n", area, size);
> INIT_LIST_HEAD(&area->list);
> area->size = size;
> list_add(&area->list, &kcov_remote_areas);
> @@ -148,9 +157,11 @@ static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_stru
>
> /*
> * We are interested in code coverage as a function of a syscall inputs,
> - * so we ignore code executed in interrupts.
> + * so we ignore code executed in interrupts, unless we are in a remote
> + * coverage collection section happening in an interrupt, which is
> + * indicated by the t->kcov_interrupt flag.
> */
> - if (!in_task())
> + if (!in_task() && !t->kcov_interrupt)
> return false;
> mode = READ_ONCE(t->kcov_mode);
> /*
> @@ -331,12 +342,12 @@ static void kcov_stop(struct task_struct *t)
> barrier();
> t->kcov_size = 0;
> t->kcov_area = NULL;
> + t->kcov = NULL;
> }
>
> static void kcov_task_reset(struct task_struct *t)
> {
> kcov_stop(t);
> - t->kcov = NULL;
> t->kcov_sequence = 0;
> t->kcov_handle = 0;
> }
> @@ -361,18 +372,18 @@ static void kcov_remote_reset(struct kcov *kcov)
> int bkt;
> struct kcov_remote *remote;
> struct hlist_node *tmp;
> + unsigned long flags;
>
> - spin_lock(&kcov_remote_lock);
> + spin_lock_irqsave(&kcov_remote_lock, flags);
> hash_for_each_safe(kcov_remote_map, bkt, tmp, remote, hnode) {
> if (remote->kcov != kcov)
> continue;
> - kcov_debug("removing handle %llx\n", remote->handle);
> hash_del(&remote->hnode);
> kfree(remote);
> }
> /* Do reset before unlock to prevent races with kcov_remote_start(). */
> kcov_reset(kcov);
> - spin_unlock(&kcov_remote_lock);
> + spin_unlock_irqrestore(&kcov_remote_lock, flags);
> }
>
> static void kcov_disable(struct task_struct *t, struct kcov *kcov)
> @@ -401,12 +412,13 @@ static void kcov_put(struct kcov *kcov)
> void kcov_task_exit(struct task_struct *t)
> {
> struct kcov *kcov;
> + unsigned long flags;
>
> kcov = t->kcov;
> if (kcov == NULL)
> return;
>
> - spin_lock(&kcov->lock);
> + spin_lock_irqsave(&kcov->lock, flags);
> kcov_debug("t = %px, kcov->t = %px\n", t, kcov->t);
> /*
> * For KCOV_ENABLE devices we want to make sure that t->kcov->t == t,
> @@ -430,12 +442,12 @@ void kcov_task_exit(struct task_struct *t)
> * By combining all three checks into one we get:
> */
> if (WARN_ON(kcov->t != t)) {
> - spin_unlock(&kcov->lock);
> + spin_unlock_irqrestore(&kcov->lock, flags);
> return;
> }
> /* Just to not leave dangling references behind. */
> kcov_disable(t, kcov);
> - spin_unlock(&kcov->lock);
> + spin_unlock_irqrestore(&kcov->lock, flags);
> kcov_put(kcov);
> }
>
> @@ -446,12 +458,13 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
> struct kcov *kcov = vma->vm_file->private_data;
> unsigned long size, off;
> struct page *page;
> + unsigned long flags;
>
> area = vmalloc_user(vma->vm_end - vma->vm_start);
> if (!area)
> return -ENOMEM;
>
> - spin_lock(&kcov->lock);
> + spin_lock_irqsave(&kcov->lock, flags);
> size = kcov->size * sizeof(unsigned long);
> if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
> vma->vm_end - vma->vm_start != size) {
> @@ -461,7 +474,7 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
> if (!kcov->area) {
> kcov->area = area;
> vma->vm_flags |= VM_DONTEXPAND;
> - spin_unlock(&kcov->lock);
> + spin_unlock_irqrestore(&kcov->lock, flags);
> for (off = 0; off < size; off += PAGE_SIZE) {
> page = vmalloc_to_page(kcov->area + off);
> if (vm_insert_page(vma, vma->vm_start + off, page))
> @@ -470,7 +483,7 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
> return 0;
> }
> exit:
> - spin_unlock(&kcov->lock);
> + spin_unlock_irqrestore(&kcov->lock, flags);
> vfree(area);
> return res;
> }
> @@ -550,10 +563,10 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
> int mode, i;
> struct kcov_remote_arg *remote_arg;
> struct kcov_remote *remote;
> + unsigned long flags;
>
> switch (cmd) {
> case KCOV_INIT_TRACE:
> - kcov_debug("KCOV_INIT_TRACE\n");
> /*
> * Enable kcov in trace mode and setup buffer size.
> * Must happen before anything else.
> @@ -572,7 +585,6 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
> kcov->mode = KCOV_MODE_INIT;
> return 0;
> case KCOV_ENABLE:
> - kcov_debug("KCOV_ENABLE\n");
> /*
> * Enable coverage for the current task.
> * At this point user must have been enabled trace mode,
> @@ -598,7 +610,6 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
> kcov_get(kcov);
> return 0;
> case KCOV_DISABLE:
> - kcov_debug("KCOV_DISABLE\n");
> /* Disable coverage for the current task. */
> unused = arg;
> if (unused != 0 || current->kcov != kcov)
> @@ -610,7 +621,6 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
> kcov_put(kcov);
> return 0;
> case KCOV_REMOTE_ENABLE:
> - kcov_debug("KCOV_REMOTE_ENABLE\n");
> if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
> return -EINVAL;
> t = current;
> @@ -627,41 +637,42 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
> kcov->t = t;
> kcov->remote = true;
> kcov->remote_size = remote_arg->area_size;
> - spin_lock(&kcov_remote_lock);
> + spin_lock_irqsave(&kcov_remote_lock, flags);
> for (i = 0; i < remote_arg->num_handles; i++) {
> - kcov_debug("handle %llx\n", remote_arg->handles[i]);
> if (!kcov_check_handle(remote_arg->handles[i],
> false, true, false)) {
> - spin_unlock(&kcov_remote_lock);
> + spin_unlock_irqrestore(&kcov_remote_lock,
> + flags);
> kcov_disable(t, kcov);
> return -EINVAL;
> }
> remote = kcov_remote_add(kcov, remote_arg->handles[i]);
> if (IS_ERR(remote)) {
> - spin_unlock(&kcov_remote_lock);
> + spin_unlock_irqrestore(&kcov_remote_lock,
> + flags);
> kcov_disable(t, kcov);
> return PTR_ERR(remote);
> }
> }
> if (remote_arg->common_handle) {
> - kcov_debug("common handle %llx\n",
> - remote_arg->common_handle);
> if (!kcov_check_handle(remote_arg->common_handle,
> true, false, false)) {
> - spin_unlock(&kcov_remote_lock);
> + spin_unlock_irqrestore(&kcov_remote_lock,
> + flags);
> kcov_disable(t, kcov);
> return -EINVAL;
> }
> remote = kcov_remote_add(kcov,
> remote_arg->common_handle);
> if (IS_ERR(remote)) {
> - spin_unlock(&kcov_remote_lock);
> + spin_unlock_irqrestore(&kcov_remote_lock,
> + flags);
> kcov_disable(t, kcov);
> return PTR_ERR(remote);
> }
> t->kcov_handle = remote_arg->common_handle;
> }
> - spin_unlock(&kcov_remote_lock);
> + spin_unlock_irqrestore(&kcov_remote_lock, flags);
> /* Put either in kcov_task_exit() or in KCOV_DISABLE. */
> kcov_get(kcov);
> return 0;
> @@ -677,6 +688,7 @@ static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
> struct kcov_remote_arg *remote_arg = NULL;
> unsigned int remote_num_handles;
> unsigned long remote_arg_size;
> + unsigned long flags;
>
> if (cmd == KCOV_REMOTE_ENABLE) {
> if (get_user(remote_num_handles, (unsigned __user *)(arg +
> @@ -697,9 +709,9 @@ static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
> }
>
> kcov = filep->private_data;
> - spin_lock(&kcov->lock);
> + spin_lock_irqsave(&kcov->lock, flags);
> res = kcov_ioctl_locked(kcov, cmd, arg);
> - spin_unlock(&kcov->lock);
> + spin_unlock_irqrestore(&kcov->lock, flags);
>
> kfree(remote_arg);
>
> @@ -716,8 +728,8 @@ static const struct file_operations kcov_fops = {
>
> /*
> * kcov_remote_start() and kcov_remote_stop() can be used to annotate a section
> - * of code in a kernel background thread to allow kcov to be used to collect
> - * coverage from that part of code.
> + * of code in a kernel background thread or in an interrupt to allow kcov to be
> + * used to collect coverage from that part of code.
> *
> * The handle argument of kcov_remote_start() identifies a code section that is
> * used for coverage collection. A userspace process passes this handle to
> @@ -728,9 +740,9 @@ static const struct file_operations kcov_fops = {
> * the type of the kernel thread whose code is being annotated.
> *
> * For global kernel threads that are spawned in a limited number of instances
> - * (e.g. one USB hub_event() worker thread is spawned per USB HCD), each
> - * instance must be assigned a unique 4-byte instance id. The instance id is
> - * then combined with a 1-byte subsystem id to get a handle via
> + * (e.g. one USB hub_event() worker thread is spawned per USB HCD) and for
> + * interrupts, each instance must be assigned a unique 4-byte instance id. The
> + * instance id is then combined with a 1-byte subsystem id to get a handle via
> * kcov_remote_handle(subsystem_id, instance_id).
> *
> * For local kernel threads that are spawned from system calls handler when a
> @@ -749,13 +761,48 @@ static const struct file_operations kcov_fops = {
> *
> * See Documentation/dev-tools/kcov.rst for more details.
> *
> - * Internally, this function looks up the kcov device associated with the
> + * Internally, kcov_remote_start() looks up the kcov device associated with the
> * provided handle, allocates an area for coverage collection, and saves the
> * pointers to kcov and area into the current task_struct to allow coverage to
> * be collected via __sanitizer_cov_trace_pc()
> * In turns kcov_remote_stop() clears those pointers from task_struct to stop
> * collecting coverage and copies all collected coverage into the kcov area.
> */
> +
> +void kcov_remote_swap_irq(struct task_struct *t,
> + struct kcov_remote_irq_data *irq)
> +{
> + t->kcov = xchg(&irq->kcov, t->kcov);
> + t->kcov_size = xchg(&irq->size, t->kcov_size);
> + t->kcov_area = xchg(&irq->area, t->kcov_area);
> + t->kcov_mode = xchg(&irq->mode, t->kcov_mode);
> +}
> +
> +bool kcov_remote_start_irq(struct task_struct *t)
> +{
> + struct kcov_remote_irq_data *irq = &get_cpu_var(kcov_remote_irq);
> +
> + if (t->kcov_interrupt) {
> + /* Nested interrupt. */
> + put_cpu_var(kcov_remote_irq);
> + return false;
> + }
> + t->kcov_interrupt = true;
> + kcov_remote_swap_irq(t, irq);
> + put_cpu_var(kcov_remote_irq);
> + return true;
> +}
> +
> +void kcov_remote_stop_irq(struct task_struct *t)
> +{
> + struct kcov_remote_irq_data *irq = &get_cpu_var(kcov_remote_irq);
> +
> + kcov_remote_swap_irq(t, irq);
> + t->kcov_interrupt = false;
> + local_irq_restore(irq->flags);
> + put_cpu_var(kcov_remote_irq);
> +}
> +
> void kcov_remote_start(u64 handle)
> {
> struct kcov_remote *remote;
> @@ -764,28 +811,32 @@ void kcov_remote_start(u64 handle)
> unsigned int size;
> enum kcov_mode mode;
> int sequence;
> + unsigned long flags;
>
> if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
> return;
> - if (WARN_ON(!in_task()))
> + if (WARN_ON(in_nmi()))
> return;
> t = current;
> /*
> - * Check that kcov_remote_start is not called twice
> - * nor called by user tasks (with enabled kcov).
> + * Check that kcov_remote_start is not called twice in background
> + * threads nor called by user tasks (with enabled kcov).
> */
> - if (WARN_ON(t->kcov))
> + if (WARN_ON(in_task() && t->kcov))
> return;
>
> - kcov_debug("handle = %llx\n", handle);
> -
> - spin_lock(&kcov_remote_lock);
> + spin_lock_irqsave(&kcov_remote_lock, flags);
> remote = kcov_remote_find(handle);
> if (!remote) {
> - kcov_debug("no remote found");
> - spin_unlock(&kcov_remote_lock);
> + spin_unlock_irqrestore(&kcov_remote_lock, flags);
> return;
> }
> + if (!in_task() && !kcov_remote_start_irq(t)) {
> + spin_unlock_irqrestore(&kcov_remote_lock, flags);
> + return;
> + }
> + kcov_debug("handle = %llx, context: %s\n", handle,
> + in_task() ? "task" : "irq");
> /* Put in kcov_remote_stop(). */
> kcov_get(remote->kcov);
> t->kcov = remote->kcov;
> @@ -793,11 +844,19 @@ void kcov_remote_start(u64 handle)
> * Read kcov fields before unlock to prevent races with
> * KCOV_DISABLE / kcov_remote_reset().
> */
> - size = remote->kcov->remote_size;
> + size = min_t(unsigned int, remote->kcov->remote_size,
> + CONFIG_KCOV_IRQ_AREA_SIZE);
> mode = remote->kcov->mode;
> sequence = remote->kcov->sequence;
> - area = kcov_remote_area_get(size);
> - spin_unlock(&kcov_remote_lock);
> + if (in_task()) {
> + area = kcov_remote_area_get(size);
> + spin_unlock_irqrestore(&kcov_remote_lock, flags);
> + } else {
> + area = *this_cpu_ptr(&kcov_irq_area);
> + /* Flags are restored by kcov_remote_stop_irq(). */
> + this_cpu_ptr(&kcov_remote_irq)->flags = flags;
> + spin_unlock(&kcov_remote_lock);
> + }
>
> if (!area) {
> area = vmalloc(size * sizeof(unsigned long));
> @@ -810,8 +869,6 @@ void kcov_remote_start(u64 handle)
> /* Reset coverage size. */
> *(u64 *)area = 0;
>
> - kcov_debug("area = %px, size = %u", area, size);
> -
> kcov_start(t, size, area, mode, sequence);
>
> }
> @@ -880,30 +937,30 @@ void kcov_remote_stop(void)
> void *area = t->kcov_area;
> unsigned int size = t->kcov_size;
> int sequence = t->kcov_sequence;
> + unsigned long flags;
>
> - if (!kcov) {
> - kcov_debug("no kcov found\n");
> + if (!kcov)
> return;
> - }
>
> kcov_stop(t);
> - t->kcov = NULL;
>
> - spin_lock(&kcov->lock);
> + spin_lock_irqsave(&kcov->lock, flags);
> /*
> * KCOV_DISABLE could have been called between kcov_remote_start()
> - * and kcov_remote_stop(), hence the check.
> + * and kcov_remote_stop(), hence the sequence check.
> */
> - kcov_debug("move if: %d == %d && %d\n",
> - sequence, kcov->sequence, (int)kcov->remote);
> if (sequence == kcov->sequence && kcov->remote)
> kcov_move_area(kcov->mode, kcov->area, kcov->size, area);
> - spin_unlock(&kcov->lock);
> + spin_unlock_irqrestore(&kcov->lock, flags);
>
> - spin_lock(&kcov_remote_lock);
> - kcov_remote_area_put(area, size);
> - spin_unlock(&kcov_remote_lock);
> + if (in_task()) {
> + spin_lock_irqsave(&kcov_remote_lock, flags);
> + kcov_remote_area_put(area, size);
> + spin_unlock_irqrestore(&kcov_remote_lock, flags);
> + } else
> + kcov_remote_stop_irq(t);
>
> + /* Get in kcov_remote_start(). */
> kcov_put(kcov);
Is it OK to call kcov_put from interrupts?
> }
> EXPORT_SYMBOL(kcov_remote_stop);
> @@ -917,6 +974,19 @@ EXPORT_SYMBOL(kcov_common_handle);
>
> static int __init kcov_init(void)
> {
> + int cpu;
> +
> + for_each_possible_cpu(cpu) {
> + void **area = per_cpu_ptr(&kcov_irq_area, cpu);
> +
> + *area = vmalloc(CONFIG_KCOV_IRQ_AREA_SIZE *
> + sizeof(unsigned long));
> + if (!*area) {
> + kcov_err("failed to allocate per-cpu area\n");
> + return -ENOMEM;
> + }
> + }
> +
> /*
> * The kcov debugfs file won't ever get removed and thus,
> * there is no need to protect it against removal races. The
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index d1842fe756d5..03f98c463a9e 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1695,6 +1695,15 @@ config KCOV_INSTRUMENT_ALL
> filesystem fuzzing with AFL) then you will want to enable coverage
> for more specific subsets of files, and should say n here.
>
> +config KCOV_IRQ_AREA_SIZE
> + hex "Size of interrupt coverage collection area in words"
> + depends on KCOV
> + default 0x40000
> + help
> + KCOV uses preallocated per-cpu areas to collect coverage from
> + interrupts. This specifies the size of those areas in the number
> + of unsigned long words.
> +
> menuconfig RUNTIME_TESTING_MENU
> bool "Runtime Testing"
> def_bool y
> --
> 2.24.1.735.g03f4e72817-goog
>
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