[PATCH] kcov, usb, vhost: specify contexts for remote coverage sections
From: Andrey Konovalov <hidden>
Date: 2020-10-07 17:30:58
Also in:
lkml
Subsystem:
documentation, documentation process, kcov, the rest, usb subsystem, virtio host (vhost) · Maintainers:
Jonathan Corbet, Linus Torvalds, Greg Kroah-Hartman, "Michael S. Tsirkin", Jason Wang
Currently there's a KCOV remote coverage collection section in __usb_hcd_giveback_urb(). Initially that section was added based on the assumption that usb_hcd_giveback_urb() can only be called in interrupt context as indicated by a comment before it. As it turns out, it's actually valid to call usb_hcd_giveback_urb() in task context, provided that the caller turned off the interrupts; USB/IP actually does that. This can lead to a nested KCOV remote coverage collection sections both trying to collect coverage in task context. This isn't supported by KCOV, and leads to a WARNING. The approach this patch takes is to annotate every call of kcov_remote_*() callbacks with the context those callbacks are supposed to be executed in. If the current context doesn't match the mask provided to a callback, that callback is ignored. KCOV currently only supports collecting remote coverage in two contexts: task and softirq. As the result, the coverage from USB/IP related usb_hcd_giveback_urb() calls won't be collected, but the WARNING is fixed. A potential future improvement would be to support nested remote coverage collection sections, but this patch doesn't address that. Signed-off-by: Andrey Konovalov <redacted> --- Documentation/dev-tools/kcov.rst | 5 +++++ drivers/usb/core/hcd.c | 4 ++-- drivers/usb/core/hub.c | 4 ++-- drivers/vhost/vhost.c | 5 +++-- include/linux/kcov.h | 24 ++++++++++++++---------- kernel/kcov.c | 16 ++++++++++++---- 6 files changed, 38 insertions(+), 20 deletions(-)
diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst
index 8548b0b04e43..99fda94a34c5 100644
--- a/Documentation/dev-tools/kcov.rst
+++ b/Documentation/dev-tools/kcov.rst@@ -235,6 +235,11 @@ saved to the kcov_handle field in the current task_struct and needs to be passed to the newly spawned threads via custom annotations. Those threads should in turn be annotated with kcov_remote_start()/kcov_remote_stop(). +Besides a handle, kcov_remote_start()/kcov_remote_stop() annotations accept +a context mask. This mask describes the contexts in which these annotations +should be applied. E.g. specifying KCOV_CONTEXT_SOFTIRQ will result in the +corresponding annotations being ignored in any context other than softirq. + Internally kcov stores handles as u64 integers. The top byte of a handle is used to denote the id of a subsystem that this handle belongs to, and the lower 4 bytes are used to denote the id of a thread instance within
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index a33b849e8beb..1b090e3218a8 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c@@ -1646,9 +1646,9 @@ static void __usb_hcd_giveback_urb(struct urb *urb) /* pass ownership to the completion handler */ urb->status = status; - kcov_remote_start_usb((u64)urb->dev->bus->busnum); + kcov_remote_start_usb((u64)urb->dev->bus->busnum, KCOV_CONTEXT_SOFTIRQ); urb->complete(urb); - kcov_remote_stop(); + kcov_remote_stop(KCOV_CONTEXT_SOFTIRQ); usb_anchor_resume_wakeups(anchor); atomic_dec(&urb->use_count);
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 5b768b80d1ee..d17db72dd020 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c@@ -5509,7 +5509,7 @@ static void hub_event(struct work_struct *work) hub_dev = hub->intfdev; intf = to_usb_interface(hub_dev); - kcov_remote_start_usb((u64)hdev->bus->busnum); + kcov_remote_start_usb((u64)hdev->bus->busnum, KCOV_CONTEXT_TASK); dev_dbg(hub_dev, "state %d ports %d chg %04x evt %04x\n", hdev->state, hdev->maxchild,
@@ -5618,7 +5618,7 @@ static void hub_event(struct work_struct *work) usb_autopm_put_interface(intf); kref_put(&hub->kref, hub_release); - kcov_remote_stop(); + kcov_remote_stop(KCOV_CONTEXT_TASK); } static const struct usb_device_id hub_id_table[] = {
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b45519ca66a7..8913de414e89 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c@@ -363,9 +363,10 @@ static int vhost_worker(void *data) llist_for_each_entry_safe(work, work_next, node, node) { clear_bit(VHOST_WORK_QUEUED, &work->flags); __set_current_state(TASK_RUNNING); - kcov_remote_start_common(dev->kcov_handle); + kcov_remote_start_common(dev->kcov_handle, + KCOV_CONTEXT_TASK); work->fn(work); - kcov_remote_stop(); + kcov_remote_stop(KCOV_CONTEXT_TASK); if (need_resched()) schedule(); }
diff --git a/include/linux/kcov.h b/include/linux/kcov.h
index a10e84707d82..507003038918 100644
--- a/include/linux/kcov.h
+++ b/include/linux/kcov.h@@ -22,6 +22,10 @@ enum kcov_mode { KCOV_MODE_TRACE_CMP = 3, }; +#define KCOV_CONTEXT_TASK (1u << 0) +#define KCOV_CONTEXT_SOFTIRQ (1u << 1) +#define KCOV_CONTEXT_MASK (KCOV_CONTEXT_TASK | KCOV_CONTEXT_SOFTIRQ) + #define KCOV_IN_CTXSW (1 << 30) void kcov_task_init(struct task_struct *t);
@@ -38,18 +42,18 @@ do { \ } while (0) /* See Documentation/dev-tools/kcov.rst for usage details. */ -void kcov_remote_start(u64 handle); -void kcov_remote_stop(void); +void kcov_remote_start(u64 handle, unsigned int context); +void kcov_remote_stop(unsigned int context); u64 kcov_common_handle(void); -static inline void kcov_remote_start_common(u64 id) +static inline void kcov_remote_start_common(u64 id, unsigned int context) { - kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id)); + kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id), context); } -static inline void kcov_remote_start_usb(u64 id) +static inline void kcov_remote_start_usb(u64 id, unsigned int context) { - kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_USB, id)); + kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_USB, id), context); } #else
@@ -58,14 +62,14 @@ static inline void kcov_task_init(struct task_struct *t) {} static inline void kcov_task_exit(struct task_struct *t) {} static inline void kcov_prepare_switch(struct task_struct *t) {} static inline void kcov_finish_switch(struct task_struct *t) {} -static inline void kcov_remote_start(u64 handle) {} -static inline void kcov_remote_stop(void) {} +static inline void kcov_remote_start(u64 handle, unsigned int context) {} +static inline void kcov_remote_stop(unsigned int context) {} static inline u64 kcov_common_handle(void) { return 0; } -static inline void kcov_remote_start_common(u64 id) {} -static inline void kcov_remote_start_usb(u64 id) {} +static inline void kcov_remote_start_common(u64 id, unsigned int context) {} +static inline void kcov_remote_start_usb(u64 id, unsigned int context) {} #endif /* CONFIG_KCOV */ #endif /* _LINUX_KCOV_H */
diff --git a/kernel/kcov.c b/kernel/kcov.c
index 6b8368be89c8..911bece5242e 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c@@ -808,7 +808,7 @@ static void kcov_remote_softirq_stop(struct task_struct *t) } } -void kcov_remote_start(u64 handle) +void kcov_remote_start(u64 handle, unsigned int context) { struct task_struct *t = current; struct kcov_remote *remote;
@@ -821,7 +821,11 @@ void kcov_remote_start(u64 handle) if (WARN_ON(!kcov_check_handle(handle, true, true, true))) return; - if (!in_task() && !in_serving_softirq()) + if (WARN_ON((context & ~KCOV_CONTEXT_MASK) || !context)) + return; + if ((context & KCOV_CONTEXT_TASK) && !in_task()) + return; + if ((context & KCOV_CONTEXT_SOFTIRQ) && !in_softirq()) return; local_irq_save(flags);
@@ -952,7 +956,7 @@ static void kcov_move_area(enum kcov_mode mode, void *dst_area, } /* See the comment before kcov_remote_start() for usage details. */ -void kcov_remote_stop(void) +void kcov_remote_stop(unsigned int context) { struct task_struct *t = current; struct kcov *kcov;
@@ -962,7 +966,11 @@ void kcov_remote_stop(void) int sequence; unsigned long flags; - if (!in_task() && !in_serving_softirq()) + if (WARN_ON((context & ~KCOV_CONTEXT_MASK) || !context)) + return; + if ((context & KCOV_CONTEXT_TASK) && !in_task()) + return; + if ((context & KCOV_CONTEXT_SOFTIRQ) && !in_softirq()) return; local_irq_save(flags);
--
2.28.0.806.g8561365e88-goog