[PATCH v5 5/8] perf/uprobe: split uprobe_unregister()

Andrii Nakryiko
2024-09-03T17:46:24Z

From: Peter Zijlstra <peterz@infradead.org>

With uprobe_unregister() having grown a synchronize_srcu(), it becomes
fairly slow to call. Esp. since both users of this API call it in a
loop.

Peel off the sync_srcu() and do it once, after the loop.

We also need to add uprobe_unregister_sync() into uprobe_register()'s
error handling path, as we need to be careful about returning to the
caller before we have a guarantee that partially attached consumer won't
be called anymore. This is an unlikely slow path and this should be
totally fine to be slow in the case of a failed attach.

Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Co-developed-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
include/linux/uprobes.h | 8 +++++--
kernel/events/uprobes.c | 21 +++++++++++++------
kernel/trace/bpf_trace.c | 5 ++++-
kernel/trace/trace_uprobe.c | 6 +++++-
.../selftests/bpf/bpf_testmod/bpf_testmod.c | 3 ++-
5 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 2785d1bedb74..968230d81798 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -116,7 +116,8 @@ extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_t);
extern struct uprobe *uprobe_register(struct inode *inode, loff_t offset, loff_t ref_ctr_offset, struct uprobe_consumer *uc);
extern int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool);
-extern void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc);
+extern void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc);
+extern void uprobe_unregister_sync(void);
extern int uprobe_mmap(struct vm_area_struct *vma);
extern void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end);
extern void uprobe_start_dup_mmap(void);
@@ -165,7 +166,10 @@ uprobe_apply(struct uprobe* uprobe, struct uprobe_consumer *uc, bool add)
return -ENOSYS;
}
static inline void
-uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
+uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc)
+{
+}
+static inline void uprobe_unregister_sync(void)
{
}
static inline int uprobe_mmap(struct vm_area_struct *vma)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 97e58d160647..e9b755ddf960 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1105,11 +1105,11 @@ register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new)
}

/**
- * uprobe_unregister - unregister an already registered probe.
+ * uprobe_unregister_nosync - unregister an already registered probe.
* @uprobe: uprobe to remove
* @uc: identify which probe if multiple probes are colocated.
*/
-void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
+void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc)
{
int err;

@@ -1121,12 +1121,15 @@ void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
/* TODO : cant unregister? schedule a worker thread */
if (unlikely(err)) {
uprobe_warn(current, "unregister, leaking uprobe");
- goto out_sync;
+ return;
}

put_uprobe(uprobe);
+}
+EXPORT_SYMBOL_GPL(uprobe_unregister_nosync);

-out_sync:
+void uprobe_unregister_sync(void)
+{
/*
* Now that handler_chain() and handle_uretprobe_chain() iterate over
* uprobe->consumers list under RCU protection without holding
@@ -1138,7 +1141,7 @@ void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
*/
synchronize_srcu(&uprobes_srcu);
}
-EXPORT_SYMBOL_GPL(uprobe_unregister);
+EXPORT_SYMBOL_GPL(uprobe_unregister_sync);

/**
* uprobe_register - register a probe
@@ -1196,7 +1199,13 @@ struct uprobe *uprobe_register(struct inode *inode,
up_write(&uprobe->register_rwsem);

if (ret) {
- uprobe_unregister(uprobe, uc);
+ uprobe_unregister_nosync(uprobe, uc);
+ /*
+ * Registration might have partially succeeded, so we can have
+ * this consumer being called right at this time. We need to
+ * sync here. It's ok, it's unlikely slow path.
+ */
+ uprobe_unregister_sync();
return ERR_PTR(ret);
}

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 73c570b5988b..6b632710c98e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3184,7 +3184,10 @@ static void bpf_uprobe_unregister(struct bpf_uprobe *uprobes, u32 cnt)
u32 i;

for (i = 0; i < cnt; i++)
- uprobe_unregister(uprobes[i].uprobe, &uprobes[i].consumer);
+ uprobe_unregister_nosync(uprobes[i].uprobe, &uprobes[i].consumer);
+
+ if (cnt)
+ uprobe_unregister_sync();
}

static void bpf_uprobe_multi_link_release(struct bpf_link *link)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 7eb79e0a5352..f7443e996b1b 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -1097,6 +1097,7 @@ static int trace_uprobe_enable(struct trace_uprobe *tu, filter_func_t filter)
static void __probe_event_disable(struct trace_probe *tp)
{
struct trace_uprobe *tu;
+ bool sync = false;

tu = container_of(tp, struct trace_uprobe, tp);
WARN_ON(!uprobe_filter_is_empty(tu->tp.event->filter));
@@ -1105,9 +1106,12 @@ static void __probe_event_disable(struct trace_probe *tp)
if (!tu->uprobe)
continue;

- uprobe_unregister(tu->uprobe, &tu->consumer);
+ uprobe_unregister_nosync(tu->uprobe, &tu->consumer);
+ sync = true;
tu->uprobe = NULL;
}
+ if (sync)
+ uprobe_unregister_sync();
}

static int probe_event_enable(struct trace_event_call *call,
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 3c0515a27842..1fc16657cf42 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -475,7 +475,8 @@ static void testmod_unregister_uprobe(void)
mutex_lock(&testmod_uprobe_mutex);

if (uprobe.uprobe) {
- uprobe_unregister(uprobe.uprobe, &uprobe.consumer);
+ uprobe_unregister_nosync(uprobe.uprobe, &uprobe.consumer);
+ uprobe_unregister_sync();
path_put(&uprobe.path);
uprobe.uprobe = NULL;
}
--
2.43.5