linux-stable.git/mm/backing-dev.c, branch v5.9.8

writeback: remove struct bdi_writeback_congested

2020-07-08T23:05:53+00:00

We never set any congested bits in the group writeback instances of it.
And for the simpler bdi-wide case a simple scalar field is all that
that is needed.

Signed-off-by: Christoph Hellwig 
Signed-off-by: Jens Axboe

writeback: remove {set,clear}_wb_congested

2020-07-08T23:05:53+00:00

Just merge them into their only callers.

Signed-off-by: Christoph Hellwig 
Signed-off-by: Jens Axboe

bdi: remove the name field in struct backing_dev_info

2020-05-09T22:15:13+00:00

The name is only printed for a not registered bdi in writeback.  Use the
device name there as is more useful anyway for the unlike case that the
warning triggers.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Jan Kara 
Reviewed-by: Greg Kroah-Hartman 
Reviewed-by: Bart Van Assche 
Signed-off-by: Jens Axboe

bdi: simplify bdi_alloc

2020-05-09T22:15:13+00:00

Merge the _node vs normal version and drop the superflous gfp_t argument.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Jan Kara 
Reviewed-by: Greg Kroah-Hartman 
Reviewed-by: Bart Van Assche 
Signed-off-by: Jens Axboe

bdi: remove bdi_register_owner

2020-05-09T22:15:13+00:00

Split out a new bdi_set_owner helper to set the owner, and move the policy
for creating the bdi name back into genhd.c, where it belongs.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Jan Kara 
Reviewed-by: Greg Kroah-Hartman 
Reviewed-by: Bart Van Assche 
Signed-off-by: Jens Axboe

bdi: unexport bdi_register_va

2020-05-09T22:15:13+00:00

bdi_register_va is only used by super.c, which can't be modular.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Jan Kara 
Reviewed-by: Greg Kroah-Hartman 
Reviewed-by: Bart Van Assche 
Signed-off-by: Jens Axboe

bdi: add a ->dev_name field to struct backing_dev_info

2020-05-09T22:07:57+00:00

Cache a copy of the name for the life time of the backing_dev_info
structure so that we can reference it even after unregistering.

Fixes: 68f23b89067f ("memcg: fix a crash in wb_workfn when a device disappears")
Reported-by: Yufen Yu 
Signed-off-by: Christoph Hellwig 
Reviewed-by: Jan Kara 
Reviewed-by: Bart Van Assche 
Signed-off-by: Jens Axboe

bdi: move bdi_dev_name out of line

2020-05-07T14:45:47+00:00

bdi_dev_name is not a fast path function, move it out of line.  This
prepares for using it from modular callers without having to export
an implementation detail like bdi_unknown_name.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Jan Kara 
Reviewed-by: Greg Kroah-Hartman 
Reviewed-by: Bart Van Assche 
Signed-off-by: Jens Axboe

blkcg: rename blkcg->cgwb_refcnt to ->online_pin and always use it

2020-04-01T20:56:42+00:00

blkcg->cgwb_refcnt is used to delay blkcg offlining so that blkgs
don't get offlined while there are active cgwbs on them.  However, it
ends up making offlining unordered sometimes causing parents to be
offlined before children.

To fix it, we want child blkcgs to pin the parents' online states
turning the refcnt into a more generic online pinning mechanism.

In prepartion,

* blkcg->cgwb_refcnt -> blkcg->online_pin
* blkcg_cgwb_get/put() -> blkcg_pin/unpin_online()
* Take them out of CONFIG_CGROUP_WRITEBACK

Signed-off-by: Tejun Heo 
Signed-off-by: Jens Axboe

memcg: fix a crash in wb_workfn when a device disappears

2020-01-31T18:30:36+00:00

Without memcg, there is a one-to-one mapping between the bdi and
bdi_writeback structures.  In this world, things are fairly
straightforward; the first thing bdi_unregister() does is to shutdown
the bdi_writeback structure (or wb), and part of that writeback ensures
that no other work queued against the wb, and that the wb is fully
drained.

With memcg, however, there is a one-to-many relationship between the bdi
and bdi_writeback structures; that is, there are multiple wb objects
which can all point to a single bdi.  There is a refcount which prevents
the bdi object from being released (and hence, unregistered).  So in
theory, the bdi_unregister() *should* only get called once its refcount
goes to zero (bdi_put will drop the refcount, and when it is zero,
release_bdi gets called, which calls bdi_unregister).

Unfortunately, del_gendisk() in block/gen_hd.c never got the memo about
the Brave New memcg World, and calls bdi_unregister directly.  It does
this without informing the file system, or the memcg code, or anything
else.  This causes the root wb associated with the bdi to be
unregistered, but none of the memcg-specific wb's are shutdown.  So when
one of these wb's are woken up to do delayed work, they try to
dereference their wb->bdi->dev to fetch the device name, but
unfortunately bdi->dev is now NULL, thanks to the bdi_unregister()
called by del_gendisk().  As a result, *boom*.

Fortunately, it looks like the rest of the writeback path is perfectly
happy with bdi->dev and bdi->owner being NULL, so the simplest fix is to
create a bdi_dev_name() function which can handle bdi->dev being NULL.
This also allows us to bulletproof the writeback tracepoints to prevent
them from dereferencing a NULL pointer and crashing the kernel if one is
tracing with memcg's enabled, and an iSCSI device dies or a USB storage
stick is pulled.

The most common way of triggering this will be hotremoval of a device
while writeback with memcg enabled is going on.  It was triggering
several times a day in a heavily loaded production environment.

Google Bug Id: 145475544

Link: https://lore.kernel.org/r/20191227194829.150110-1-tytso@mit.edu
Link: http://lkml.kernel.org/r/20191228005211.163952-1-tytso@mit.edu
Signed-off-by: Theodore Ts'o 
Cc: Chris Mason 
Cc: Tejun Heo 
Cc: Jens Axboe 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds