Messages in this thread Patch in this message | | | Date | Fri, 2 Jun 2023 09:32:56 -0700 | From | Boqun Feng <> | Subject | Re: [PATCH v2 5/8] rust: workqueue: add helper for defining work_struct fields |
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On Fri, Jun 02, 2023 at 08:38:56AM +0000, Alice Ryhl wrote: > Boqun Feng <boqun.feng@gmail.com> writes: > > On Thu, Jun 01, 2023 at 01:49:43PM +0000, Alice Ryhl wrote: > >> diff --git a/rust/helpers.c b/rust/helpers.c > >> index 81e80261d597..7f0c2fe2fbeb 100644 > >> --- a/rust/helpers.c > >> +++ b/rust/helpers.c > >> @@ -26,6 +26,7 @@ > >> #include <linux/spinlock.h> > >> #include <linux/sched/signal.h> > >> #include <linux/wait.h> > >> +#include <linux/workqueue.h> > >> > >> __noreturn void rust_helper_BUG(void) > >> { > >> @@ -128,6 +129,13 @@ void rust_helper_put_task_struct(struct task_struct *t) > >> } > >> EXPORT_SYMBOL_GPL(rust_helper_put_task_struct); > >> > >> +void rust_helper___INIT_WORK(struct work_struct *work, work_func_t func, > >> + bool on_stack) > >> +{ > >> + __INIT_WORK(work, func, on_stack); > > > > Note here all the work items in Rust will share the same lockdep class. > > That could be problematic: the lockdep classes for work are for > > detecting deadlocks in the following scenario: > > > > step 1: queue a work "foo", whose work function is: > > > > mutex_lock(&bar); > > do_something(...); > > mutex_unlock(&bar); > > > > step 2: in another thread do: > > > > mutex_lock(&bar); > > flush_work(foo); // wait until work "foo" is finished. > > > > if this case, if step 2 get the lock "bar" first, it's a deadlock. > > > > With the current implementation, all the work items share the same > > lockdep class, so the following will be treated as deadlock: > > > > <in work "work1"> > > mutex_lock(&bar); > > do_something(...); > > mutex_unlock(&bar); > > > > <in another thread> > > mutex_lock(&bar); > > flush_work(work2); // flush work2 intead of work1. > > > > which is a false positive. We at least need some changes in C side to > > make it work: > > > > https://lore.kernel.org/rust-for-linux/20220802015052.10452-7-ojeda@kernel.org/ > > > > however, that still has the disadvantage that all Rust work items have > > the same name for the lockdep classes.. maybe we should extend that for > > an extra "name" parameter. And then it's not necessary to be a macro. > > Yeah, I did know about this issue, but I didn't know what the best way > to fix it is. What solution would you like me to use? >
Having a init_work_with_key() function in C side:
void init_work_with_key(struct work_struct *work, bool onstack, const char *name, struct lock_class_key *key) { __init_work(work, onstack); \ work->data = (atomic_long_t) WORK_DATA_INIT(); \ lockdep_init_map(&work->lockdep_map, name, key, 0); \ INIT_LIST_HEAD(&work->entry); \ work->func = func; \ }
, and provide class key and name from Rust side.
Thoughts?
Regards, Boqun
> Alice
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