On 22.06.21 10:26, Ahmad Fatoum wrote:
> Originally, I envisioned bthreads as replacement for pollers and
> workqueues. But even without preemption, having functions you call
> possibly accessing structures you are iterating over can corrupt
> memory. This problem exists with pollers as well, but because of their
> limited scope, it's harder to shoot your foot with them, as you
> don't keep implicit state between poller activations unlike bthreads,
> which maintain their stack across context switches.
>
> Limit bthread scope instead to be a replacement for workqueues. This
> still allows us to port some classes of state-machine-in-kthread kernel
> code, while avoding the aforementioned pitfalls.
>
> Cc: Jan Luebbe <j.luebbe@xxxxxxxxxxxxxx>
> Cc: Sascha Hauer <a.hauer@xxxxxxxxxxxxxx>
Mailer daemon just told me the first character of Sascha is not an a.
Please fixup on apply (or I do with v5)
> Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
> ---
> commands/bthread.c | 5 +++++
> common/sched.c | 6 +++---
> include/slice.h | 2 --
> 3 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/commands/bthread.c b/commands/bthread.c
> index 964a1044c58b..0c9c221884e8 100644
> --- a/commands/bthread.c
> +++ b/commands/bthread.c
> @@ -10,12 +10,15 @@
> #include <command.h>
> #include <getopt.h>
> #include <clock.h>
> +#include <slice.h>
>
> static int bthread_time(void)
> {
> uint64_t start = get_time_ns();
> int i = 0;
>
> + slice_release(&command_slice);
> +
> /*
> * How many background tasks can we have in one second?
> *
> @@ -25,6 +28,8 @@ static int bthread_time(void)
> while (!is_timeout(start, SECOND))
> i++;
>
> + slice_acquire(&command_slice);
> +
> return i;
> }
>
> diff --git a/common/sched.c b/common/sched.c
> index dcf6522ac058..02582b2c5e4d 100644
> --- a/common/sched.c
> +++ b/common/sched.c
> @@ -15,12 +15,12 @@ void resched(void)
>
> command_slice_acquire();
>
> - if (run_workqueues)
> + if (run_workqueues) {
> wq_do_all_works();
> + bthread_reschedule();
> + }
>
> poller_call();
>
> command_slice_release();
> -
> - bthread_reschedule();
> }
> diff --git a/include/slice.h b/include/slice.h
> index 67d47b9082e6..6c4688e308fa 100644
> --- a/include/slice.h
> +++ b/include/slice.h
> @@ -38,8 +38,6 @@ void command_slice_release(void);
>
> #define assert_command_context() do { \
> WARN_ONCE(poller_active(), "%s called in poller\n", __func__); \
> - WARN_ONCE(IS_ENABLED(CONFIG_BTHREAD) && !bthread_is_main(current), \
> - "%s called in secondary bthread\n", __func__); \
> } while (0)
>
> #endif
>
--
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