On Tue, Jan 18, 2022 at 08:15:36PM +0000, Vladimir Kondratyev wrote:
> The branch main has been updated by wulf:
>
> URL:
> https://cgit.FreeBSD.org/src/commit/?id=02ea6033020e11afec6472bf560b0ddebd0fa97a
>
> commit 02ea6033020e11afec6472bf560b0ddebd0fa97a
> Author: Vladimir Kondratyev <[email protected]>
> AuthorDate: 2022-01-18 20:14:12 +0000
> Commit: Vladimir Kondratyev <[email protected]>
> CommitDate: 2022-01-18 20:14:12 +0000
>
> LinuxKPI: Allow spin_lock_irqsave to be called within a critical section
>
> with spinning on spin_trylock. dma-buf part of drm-kmod depends on this
> property and absence of it support results in "mi_switch: switch in a
> critical section" assertions [1][2].
>
> [1] https://github.com/freebsd/drm-kmod/issues/116
> [2] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=261166
>
> MFC after: 1 week
> Reviewed by: manu
> Differential Revision: https://reviews.freebsd.org/D33887
> ---
> .../linuxkpi/common/include/linux/spinlock.h | 27
> ++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/sys/compat/linuxkpi/common/include/linux/spinlock.h
> b/sys/compat/linuxkpi/common/include/linux/spinlock.h
> index a87cb7180b28..31d47fa73986 100644
> --- a/sys/compat/linuxkpi/common/include/linux/spinlock.h
> +++ b/sys/compat/linuxkpi/common/include/linux/spinlock.h
> @@ -37,6 +37,7 @@
> #include <sys/lock.h>
> #include <sys/mutex.h>
> #include <sys/kdb.h>
> +#include <sys/proc.h>
>
> #include <linux/compiler.h>
> #include <linux/rwlock.h>
> @@ -117,14 +118,32 @@ typedef struct {
> local_bh_disable(); \
> } while (0)
>
> -#define spin_lock_irqsave(_l, flags) do { \
> - (flags) = 0; \
> - spin_lock(_l); \
> +#define __spin_trylock_nested(_l, _n) ({ \
> + int __ret; \
> + if (SPIN_SKIP()) { \
> + __ret = 1; \
> + } else { \
> + __ret = mtx_trylock_flags(&(_l)->m, MTX_DUPOK); \
> + if (likely(__ret != 0)) \
> + local_bh_disable(); \
> + } \
> + __ret; \
> +})
> +
> +#define spin_lock_irqsave(_l, flags) do { \
> + (flags) = 0; \
> + if (unlikely(curthread->td_critnest != 0)) \
> + while (!spin_trylock(_l)) {} \
> + else \
> + spin_lock(_l); \
> } while (0)
>
> #define spin_lock_irqsave_nested(_l, flags, _n) do { \
> (flags) = 0; \
> - spin_lock_nested(_l, _n); \
> + if (unlikely(curthread->td_critnest != 0)) \
> + while (!__spin_trylock_nested(_l, _n)) {} \
> + else \
> + spin_lock_nested(_l, _n); \
> } while (0)
>
> #define spin_unlock_irqrestore(_l, flags) do { \
You are spin-waiting for blockable mutex, am I right? This means a deadlock.
Just for example, on UP machine the spinning thread could starve the thread
that owns the mutex, which never gets to the CPU.
