On Sun, 2015-01-18 at 16:22 +0000, James Bottomley wrote:
> On Mon, 2015-01-05 at 12:03 +0100, Bart Van Assche wrote:
> > Avoid that the following warning is reported when a SCSI LLD kernel
> > module is unloaded:
> >
> > WARNING: CPU: 5 PID: 228 at kernel/module.c:954 module_put+0x207/0x220()
> > Call Trace:
> > [<ffffffff814d1fcf>] dump_stack+0x4c/0x65
> > [<ffffffff81053ada>] warn_slowpath_common+0x8a/0xc0
> > [<ffffffff81053bca>] warn_slowpath_null+0x1a/0x20
> > [<ffffffff810d0507>] module_put+0x207/0x220
> > [<ffffffffa000bea8>] scsi_device_put+0x48/0x50 [scsi_mod]
> > [<ffffffffa03676d2>] scsi_disk_put+0x32/0x50 [sd_mod]
> > [<ffffffffa0368d4c>] sd_shutdown+0x8c/0x150 [sd_mod]
> > [<ffffffffa0368e79>] sd_remove+0x69/0xc0 [sd_mod]
> > [<ffffffff813457ef>] __device_release_driver+0x7f/0xf0
> > [<ffffffff81345885>] device_release_driver+0x25/0x40
> > [<ffffffff81345134>] bus_remove_device+0x124/0x1b0
> > [<ffffffff8134189e>] device_del+0x13e/0x250
> > [<ffffffffa001cdcd>] __scsi_remove_device+0xcd/0xe0 [scsi_mod]
> > [<ffffffffa001b39f>] scsi_forget_host+0x6f/0x80 [scsi_mod]
> > [<ffffffffa000d5f6>] scsi_remove_host+0x86/0x140 [scsi_mod]
> > [<ffffffffa07d5c0b>] srp_remove_work+0x9b/0x210 [ib_srp]
> > [<ffffffff8106fd28>] process_one_work+0x1d8/0x780
> > [<ffffffff810703eb>] worker_thread+0x11b/0x4a0
> > [<ffffffff81075a6f>] kthread+0xef/0x110
> > [<ffffffff814dad6c>] ret_from_fork+0x7c/0xb0
> >
> > See also patch "module: Remove stop_machine from module unloading"
> > (Masami Hiramatsu; commit e513cc1c07e2; kernel v3.19-rc1).
> >
> > Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Hannes Reinecke <hare@xxxxxxx>
> > ---
> > drivers/scsi/hosts.c | 1 +
> > drivers/scsi/scsi.c | 13 ++++---------
> > include/scsi/scsi_host.h | 3 +++
> > 3 files changed, 8 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> > index 8bb173e..e9155d0 100644
> > --- a/drivers/scsi/hosts.c
> > +++ b/drivers/scsi/hosts.c
> > @@ -380,6 +380,7 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
> >
> > shost->host_lock = &shost->default_lock;
> > spin_lock_init(shost->host_lock);
> > + atomic_set(&shost->module_refcnt, 0);
> > shost->shost_state = SHOST_CREATED;
> > INIT_LIST_HEAD(&shost->__devices);
> > INIT_LIST_HEAD(&shost->__targets);
> > diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> > index e028854..ed325d1 100644
> > --- a/drivers/scsi/scsi.c
> > +++ b/drivers/scsi/scsi.c
> > @@ -988,7 +988,8 @@ int scsi_device_get(struct scsi_device *sdev)
> > return -ENXIO;
> > /* We can fail this if we're doing SCSI operations
> > * from module exit (like cache flush) */
> > - try_module_get(sdev->host->hostt->module);
> > + if (try_module_get(sdev->host->hostt->module))
> > + atomic_inc(&sdev->host->module_refcnt);
> >
> > return 0;
> > }
> > @@ -1004,14 +1005,8 @@ EXPORT_SYMBOL(scsi_device_get);
> > */
> > void scsi_device_put(struct scsi_device *sdev)
> > {
> > -#ifdef CONFIG_MODULE_UNLOAD
> > - struct module *module = sdev->host->hostt->module;
> > -
> > - /* The module refcount will be zero if scsi_device_get()
> > - * was called from a module removal routine */
> > - if (module && module_refcount(module) != 0)
> > - module_put(module);
> > -#endif
> > + if (atomic_dec_if_positive(&sdev->host->module_refcnt) >= 0)
> > + module_put(sdev->host->hostt->module);
> > put_device(&sdev->sdev_gendev);
> > }
> > EXPORT_SYMBOL(scsi_device_put);
> > diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> > index 019e668..b8e6f01 100644
> > --- a/include/scsi/scsi_host.h
> > +++ b/include/scsi/scsi_host.h
> > @@ -566,6 +566,9 @@ struct Scsi_Host {
> > struct scsi_host_template *hostt;
> > struct scsi_transport_template *transportt;
> >
> > + /* Number of LLD kernel module references held by the SCSI core. */
> > + atomic_t module_refcnt;
> > +
> > /*
> > * Area to keep a shared tag map (if needed, will be
> > * NULL if not).
>
> This is a bit over coded for a fix. We don't need to duplicate the
> module reference, merely take into account that in the remove code
> module_refcnt() can now return -1, which we're not expecting.
>
> Masami, this looks like a nasty unintended consequence of
>
> commit e513cc1c07e2ab93a4514eec9833e031df3e30bb
> Author: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> Date: Mon Nov 10 09:30:29 2014 +1030
>
> module: Remove stop_machine from module unloading
>
> Are you sure we all should have to alter our module refcounting in
> removal routines like this? I think the better fix is having
> module_refcount() never return a negative number:
>
> unsigned long module_refcount(struct module *mod)
> {
> unsigned long ret = (unsigned long)atomic_read(&mod->refcnt);
>
> if (ret == 0)
> return ret
> return ret - MODULE_REF_BASE;
> }
>
> James
>
> ---
>
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index e028854..90dcb2f 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -1009,7 +1009,7 @@ void scsi_device_put(struct scsi_device *sdev)
>
> /* The module refcount will be zero if scsi_device_get()
> * was called from a module removal routine */
> - if (module && module_refcount(module) != 0)
> + if (module && module_refcount(module) > 0)
> module_put(module);
> #endif
> put_device(&sdev->sdev_gendev);
Actually, thought about it some more. The above won't work because
module_refcount() is returning an unsigned type, so -1 is actually the
largest integer. I think this indicates the proper fix is in
module_refcount(), I'll code it up and send it in.
James
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