[PATCH v3 tip/perf/core 1/2] uprobes: allow put_uprobe() from non-sleepable softirq context
From: Andrii Nakryiko <andrii@kernel.org>
Date: 2024-10-24 04:42:06
Also in:
bpf, lkml
Subsystem:
performance events subsystem, the rest, uprobes · Maintainers:
Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Linus Torvalds, Masami Hiramatsu, Oleg Nesterov
Currently put_uprobe() might trigger mutex_lock()/mutex_unlock(), which makes it unsuitable to be called from more restricted context like softirq. Let's make put_uprobe() agnostic to the context in which it is called, and use work queue to defer the mutex-protected clean up steps. RB tree removal step is also moved into work-deferred callback to avoid potential deadlock between softirq-based timer callback, added in the next patch, and the rest of uprobe code. We can rework locking altogher as a follow up, but that's significantly more tricky, so warrants its own patch set. For now, we need to make sure that changes in the next patch that add timer thread work correctly with existing approach, while concentrating on SRCU + timeout logic. Signed-off-by: Andrii Nakryiko <andrii@kernel.org> --- kernel/events/uprobes.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 4ef4b51776eb..d7e489246608 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c@@ -27,6 +27,7 @@ #include <linux/shmem_fs.h> #include <linux/khugepaged.h> #include <linux/rcupdate_trace.h> +#include <linux/workqueue.h> #include <linux/uprobes.h>
@@ -61,7 +62,10 @@ struct uprobe { struct list_head pending_list; struct list_head consumers; struct inode *inode; /* Also hold a ref to inode */ - struct rcu_head rcu; + union { + struct rcu_head rcu; + struct work_struct work; + }; loff_t offset; loff_t ref_ctr_offset; unsigned long flags; /* "unsigned long" so bitops work */
@@ -625,10 +629,9 @@ static void uprobe_free_rcu(struct rcu_head *rcu) kfree(uprobe); } -static void put_uprobe(struct uprobe *uprobe) +static void uprobe_free_deferred(struct work_struct *work) { - if (!refcount_dec_and_test(&uprobe->ref)) - return; + struct uprobe *uprobe = container_of(work, struct uprobe, work); write_lock(&uprobes_treelock);
@@ -652,6 +655,15 @@ static void put_uprobe(struct uprobe *uprobe) call_rcu_tasks_trace(&uprobe->rcu, uprobe_free_rcu); } +static void put_uprobe(struct uprobe *uprobe) +{ + if (!refcount_dec_and_test(&uprobe->ref)) + return; + + INIT_WORK(&uprobe->work, uprobe_free_deferred); + schedule_work(&uprobe->work); +} + static __always_inline int uprobe_cmp(const struct inode *l_inode, const loff_t l_offset, const struct uprobe *r)
--
2.43.5