[lkml]   [2020]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC 3/3] block: avoid deferral of blk_release_queue() work
On Thu, Apr 02, 2020 at 04:49:37PM +0200, Nicolai Stange wrote:
> Bart Van Assche <> writes:
> > On 2020-04-01 17:00, Luis Chamberlain wrote:
> > The description of this patch mentions a single blk_release_queue() call
> > that happened in the past from a context from which sleeping is not
> > allowed and from which sleeping is allowed today. Have all other
> > blk_release_queue() / blk_put_queue() calls been verified to see whether
> > none of these happens from a context from which sleeping is not allowed?
> I've just done this today and found the following potentially
> problematic call paths to blk_put_queue().
> 1.) mem_cgroup_throttle_swaprate() takes a spinlock and
> calls blkcg_schedule_throttle()->blk_put_queue().
> Also note that AFAICS mem_cgroup_try_charge_delay() can be called
> with GFP_ATOMIC.

I have a solution to this which would avoid having to deal with the
concern completely. I'll post in my follow up.

> 2.) scsi_unblock_requests() gets called from a lot of drivers and
> invoke blk_put_queue() through
> scsi_unblock_requests() -> scsi_run_host_queues() ->
> scsi_starved_list_run() -> blk_put_queue().

sd_probe() calls device_add_disk(), and the scsi lib also has its
own refcounting for scsi, but unless you call sd_remove() you'll be
protecting the underlying block disk and request_queue, as sd_remove()
calls the del_gendisk() which would in call call blk_unregister_queue()
which calls the last blk_put_queue(). If sd_remove() can be called from
atomic context we can also fix this, and this should be evident how in
my next follow up series of patches.


 \ /
  Last update: 2020-04-09 20:11    [W:0.103 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site