Re: [PATCH 00/11] scsi: libsas: Remove in_interrupt() check

[Jason Yan]

在 2020/12/21 18:13, John Garry 写道:
> On 18/12/2020 20:43, Ahmed S. Darwish wrote:
> > Folks,
> >
> > In the discussion about preempt count consistency across kernel
> > configurations:
> >
> >    https://lkml.kernel.org/r/20200914204209.256266093@xxxxxxxxxxxxx
> >
> > it was concluded that the usage of in_interrupt() and related context
> > checks should be removed from non-core code.
> >
> > This includes memory allocation mode decisions (GFP_*). In the long run,
> > usage of in_interrupt() and its siblings should be banned from driver
> > code completely.
> >
> > This series addresses SCSI libsas. Basically, the function:
> >
> >    => drivers/scsi/libsas/sas_init.c:
> >    struct asd_sas_event *sas_alloc_event(struct asd_sas_phy *phy)
> >    {
> >          ...
> >          gfp_t flags = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
> >          event = kmem_cache_zalloc(sas_event_cache, flags);
>
> Hi Ahmed,
>
> Firstly I would say that it would be nice to just remove all the atomic 
> context calls. But that may require significant LLDD rework and 
> participation from driver stakeholders.
>
> However, considering function sas_alloc_event() again:
>
>      gfp_t flags = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
>
>      ...
>
>      event = kmem_cache_zalloc(sas_event_cache, flags);
>      if (!event)
>          return NULL;
>
>      atomic_inc(&phy->event_nr);
>
>      if (atomic_read(&phy->event_nr) > phy->ha->event_thres) {
>          /* Code to shutdown the phy */
>      }
>
>      return event;
>
>
> So default for phy->ha->event_thres is 32, and I can't imagine that 

The default value is 1024.

> anyone has ever reconfigured this via sysfs or even required a value 
> that large. Maybe Jason (cc'ed) knows better. It's an arbitrary value to 
> say that the PHY is malfunctioning. I do note that there is the circular 
> path sas_alloc_event() -> sas_notify_phy_event() -> sas_alloc_event() 
> there also.
>
> Anyway, if the 32x event memories were per-allocated, maybe there is a 
> clean method to manage this memory, which even works in atomic context, 
> so we could avoid this rework (ignoring the context bugs you reported 
> for a moment). I do also note that the sas_event_cache size is not huge.

Pre-allocated memory is an option.(Which we have tried at the very 
beginnig by Wang Yijing.)

Or directly use GFP_ATOMIC is maybe better than passing flags from lldds.

Thanks,
Jason

> Anyway, I'll look at the rest of the series.
>
> Thanks,
> John
>
> >          ...
> >    }
> >
> > is transformed so that callers explicitly pass the gfp_t memory
> > allocation flags. Affected libsas clients are modified accordingly.
> >
> > The first six patches have "Fixes: " tags and address bugs the were
> > noticed during the context analysis.
> >
> > Thanks!
> >
> > 8<--------------
> >
> > Ahmed S. Darwish (11):
> >    Documentation: scsi: libsas: Remove notify_ha_event()
> >    scsi: libsas: Introduce a _gfp() variant of event notifiers
> >    scsi: mvsas: Pass gfp_t flags to libsas event notifiers
> >    scsi: isci: port: link down: Pass gfp_t flags
> >    scsi: isci: port: link up: Pass gfp_t flags
> >    scsi: isci: port: broadcast change: Pass gfp_t flags
> >    scsi: libsas: Pass gfp_t flags to event notifiers
> >    scsi: pm80xx: Pass gfp_t flags to libsas event notifiers
> >    scsi: aic94xx: Pass gfp_t flags to libsas event notifiers
> >    scsi: hisi_sas: Pass gfp_t flags to libsas event notifiers
> >    scsi: libsas: event notifiers: Remove non _gfp() variants
> >
> >   Documentation/scsi/libsas.rst          |  5 ++--
> >   drivers/scsi/aic94xx/aic94xx_scb.c     | 18 ++++++------
> >   drivers/scsi/hisi_sas/hisi_sas.h       |  3 +-
> >   drivers/scsi/hisi_sas/hisi_sas_main.c  | 26 ++++++++++--------
> >   drivers/scsi/hisi_sas/hisi_sas_v1_hw.c |  5 ++--
> >   drivers/scsi/hisi_sas/hisi_sas_v2_hw.c |  5 ++--
> >   drivers/scsi/hisi_sas/hisi_sas_v3_hw.c |  5 ++--
> >   drivers/scsi/isci/port.c               | 14 ++++++----
> >   drivers/scsi/libsas/sas_event.c        | 21 ++++++++------
> >   drivers/scsi/libsas/sas_init.c         | 11 ++++----
> >   drivers/scsi/libsas/sas_internal.h     |  4 +--
> >   drivers/scsi/mvsas/mv_sas.c            | 22 +++++++--------
> >   drivers/scsi/pm8001/pm8001_hwi.c       | 38 +++++++++++++-------------
> >   drivers/scsi/pm8001/pm8001_sas.c       |  8 +++---
> >   drivers/scsi/pm8001/pm80xx_hwi.c       | 30 ++++++++++----------
> >   include/scsi/libsas.h                  |  4 +--
> >   16 files changed, 116 insertions(+), 103 deletions(-)
> >
> > base-commit: 2c85ebc57b3e1817b6ce1a6b703928e113a90442
> > --
> > 2.29.2
> > .
>
> .