Make persistent grants per-queue/ring instead of per-device, so that we can
drop the 'dev_lock' and get better scalability.

Test was done based on null_blk driver:
dom0: v4.2-rc8 16vcpus 10GB "modprobe null_blk"
domu: v4.2-rc8 16vcpus 10GB

[test]
rw=read
direct=1
ioengine=libaio
bs=4k
time_based
runtime=30
filename=/dev/xvdb
numjobs=16
iodepth=64
iodepth_batch=64
iodepth_batch_complete=64
group_reporting

Queues:			  1 	   4 	  	  8 	 	 16
Iops orig(k):		810 	1064 		780 		700
Iops patched(k):	810     1230(~20%)	1024(~20%)	850(~20%)
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

We do the same exact operations a bit earlier in the
function.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

The max number of hardware queues for xen/blkfront is set by parameter
'max_queues'(default 4), while it is also capped by the max value that the
xen/blkback exposes through XenStore key 'multi-queue-max-queues'.

The negotiated number is the smaller one and would be written back to xenstore
as "multi-queue-num-queues", blkback needs to read this negotiated number.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

After patch "xen/blkfront: separate per ring information out of device
info", per-ring data is protected by a per-device lock ('io_lock').

This is not a good way and will effect the scalability, so introduce a
per-ring lock ('ring_lock').

The old 'io_lock' is renamed to 'dev_lock' which protects the ->grants list and
->persistent_gnts_c which are shared by all rings.

Note that in 'blkfront_probe' the 'blkfront_info' is setup via kzalloc
so setting ->persistent_gnts_c to zero is not needed.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Preparatory patch for multiple hardware queues (rings). The number of
rings is unconditionally set to 1, larger number will be enabled in
patch "xen/blkfront: negotiate number of queues/rings to be used with backend"
so as to make review easier.

Note that blkfront_gather_backend_features does not call
blkfront_setup_indirect anymore (as that needs to be done per ring).
That means that in blkif_recover/blkif_connect we have to do it in a loop
(bounded by nr_rings).
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Split per ring information to a new structure "blkfront_ring_info".

A ring is the representation of a hardware queue, every vbd device can associate
with one or more rings depending on how many hardware queues/rings to be used.

This patch is a preparation for supporting real multi hardware queues/rings.

We also add a backpointer to 'struct blkfront_info' (dev_info) which
is not needed (we could use containers_of) but further patch
("xen/blkfront: pseudo support for multi hardware queues/rings")
will make allocation of 'blkfront_ring_info' dynamic.
Signed-off-by: NArianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Document the multi-queue/ring feature in terms of XenStore keys to be written by
the backend and by the frontend.
Signed-off-by: NBob Liu <bob.liu@oracle.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Previously, it would only scan the entire disk if it was starting from
the very start of the disk - i.e. if the previous scan got to the end.

This was broken by refill_full_stripes(), which updates last_scanned so
that refill_dirty was never triggering the searched_from_start path.

But if we change refill_dirty() to always scan the entire disk if
necessary, regardless of what last_scanned was, the code gets cleaner
and we fix that bug too.
Signed-off-by: NKent Overstreet <kent.overstreet@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

Added a safeguard in the shutdown case. At least while not being
attached it is also possible to trigger a kernel bug by writing into
writeback_running. This change  adds the same check before trying to
wake up the thread for that case.
Signed-off-by: NStefan Bader <stefan.bader@canonical.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

Allows to use register, not register_quiet in udev to avoid "device_busy" error.
The initial patch proposed at https://lkml.org/lkml/2013/8/26/549 by Gabriel de Perthuis
<g2p.code@gmail.com> does not unlock the mutex and hangs the kernel.

See http://thread.gmane.org/gmane.linux.kernel.bcache.devel/2594 for the discussion.

Cc: Denis Bychkov <manover@gmail.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Eric Wheeler <bcache@linux.ewheeler.net>
Cc: Gabriel de Perthuis <g2p.code@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

In bcache_init() function it forgot to unregister reboot notifier if
bcache fails to unregister a block device.  This commit fixes this.
Signed-off-by: NZheng Liu <wenqing.lz@taobao.com>
Tested-by: NJoshua Schmid <jschmid@suse.com>
Tested-by: NEric Wheeler <bcache@linux.ewheeler.net>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Tested-by: NJoshua Schmid <jschmid@suse.com>
Tested-by: NEric Wheeler <bcache@linux.ewheeler.net>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

This bug can be reproduced by the following script:

  #!/bin/bash

  bcache_sysfs="/sys/fs/bcache"

  function clear_cache()
  {
  	if [ ! -e $bcache_sysfs ]; then
  		echo "no bcache sysfs"
  		exit
  	fi

  	cset_uuid=$(ls -l $bcache_sysfs|head -n 2|tail -n 1|awk '{print $9}')
  	sudo sh -c "echo $cset_uuid > /sys/block/sdb/sdb1/bcache/detach"
  	sleep 5
  	sudo sh -c "echo $cset_uuid > /sys/block/sdb/sdb1/bcache/attach"
  }

  for ((i=0;i<10;i++)); do
  	clear_cache
  done

The warning messages look like below:
[  275.948611] ------------[ cut here ]------------
[  275.963840] WARNING: at fs/sysfs/dir.c:512 sysfs_add_one+0xb8/0xd0() (Tainted: P        W
---------------   )
[  275.979253] Hardware name: Tecal RH2285
[  275.994106] sysfs: cannot create duplicate filename '/devices/pci0000:00/0000:00:09.0/0000:08:00.0/host4/target4:2:1/4:2:1:0/block/sdb/sdb1/bcache/cache'
[  276.024105] Modules linked in: bcache tcp_diag inet_diag ipmi_devintf ipmi_si ipmi_msghandler
bonding 8021q garp stp llc ipv6 ext3 jbd loop sg iomemory_vsl(P) bnx2 microcode serio_raw i2c_i801
i2c_core iTCO_wdt iTCO_vendor_support i7core_edac edac_core shpchp ext4 jbd2 mbcache megaraid_sas
pata_acpi ata_generic ata_piix dm_mod [last unloaded: scsi_wait_scan]
[  276.072643] Pid: 2765, comm: sh Tainted: P        W  ---------------    2.6.32 #1
[  276.089315] Call Trace:
[  276.105801]  [<ffffffff81070fe7>] ? warn_slowpath_common+0x87/0xc0
[  276.122650]  [<ffffffff810710d6>] ? warn_slowpath_fmt+0x46/0x50
[  276.139361]  [<ffffffff81205c08>] ? sysfs_add_one+0xb8/0xd0
[  276.156012]  [<ffffffff8120609b>] ? sysfs_do_create_link+0x12b/0x170
[  276.172682]  [<ffffffff81206113>] ? sysfs_create_link+0x13/0x20
[  276.189282]  [<ffffffffa03bda21>] ? bcache_device_link+0xc1/0x110 [bcache]
[  276.205993]  [<ffffffffa03bfa08>] ? bch_cached_dev_attach+0x478/0x4f0 [bcache]
[  276.222794]  [<ffffffffa03c4a17>] ? bch_cached_dev_store+0x627/0x780 [bcache]
[  276.239680]  [<ffffffff8116783a>] ? alloc_pages_current+0xaa/0x110
[  276.256594]  [<ffffffff81203b15>] ? sysfs_write_file+0xe5/0x170
[  276.273364]  [<ffffffff811887b8>] ? vfs_write+0xb8/0x1a0
[  276.290133]  [<ffffffff811890b1>] ? sys_write+0x51/0x90
[  276.306368]  [<ffffffff8100c072>] ? system_call_fastpath+0x16/0x1b
[  276.322301] ---[ end trace 9f5d4fcdd0c3edfb ]---
[  276.338241] ------------[ cut here ]------------
[  276.354109] WARNING: at /home/wenqing.lz/bcache/bcache/super.c:720
bcache_device_link+0xdf/0x110 [bcache]() (Tainted: P        W  ---------------   )
[  276.386017] Hardware name: Tecal RH2285
[  276.401430] Couldn't create device <-> cache set symlinks
[  276.401759] Modules linked in: bcache tcp_diag inet_diag ipmi_devintf ipmi_si ipmi_msghandler
bonding 8021q garp stp llc ipv6 ext3 jbd loop sg iomemory_vsl(P) bnx2 microcode serio_raw i2c_i801
i2c_core iTCO_wdt iTCO_vendor_support i7core_edac edac_core shpchp ext4 jbd2 mbcache megaraid_sas
pata_acpi ata_generic ata_piix dm_mod [last unloaded: scsi_wait_scan]
[  276.465477] Pid: 2765, comm: sh Tainted: P        W  ---------------    2.6.32 #1
[  276.482169] Call Trace:
[  276.498610]  [<ffffffff81070fe7>] ? warn_slowpath_common+0x87/0xc0
[  276.515405]  [<ffffffff810710d6>] ? warn_slowpath_fmt+0x46/0x50
[  276.532059]  [<ffffffffa03bda3f>] ? bcache_device_link+0xdf/0x110 [bcache]
[  276.548808]  [<ffffffffa03bfa08>] ? bch_cached_dev_attach+0x478/0x4f0 [bcache]
[  276.565569]  [<ffffffffa03c4a17>] ? bch_cached_dev_store+0x627/0x780 [bcache]
[  276.582418]  [<ffffffff8116783a>] ? alloc_pages_current+0xaa/0x110
[  276.599341]  [<ffffffff81203b15>] ? sysfs_write_file+0xe5/0x170
[  276.616142]  [<ffffffff811887b8>] ? vfs_write+0xb8/0x1a0
[  276.632607]  [<ffffffff811890b1>] ? sys_write+0x51/0x90
[  276.648671]  [<ffffffff8100c072>] ? system_call_fastpath+0x16/0x1b
[  276.664756] ---[ end trace 9f5d4fcdd0c3edfc ]---

We forget to clear BCACHE_DEV_UNLINK_DONE flag in bcache_device_attach()
function when we attach a backing device first time.  After detaching this
backing device, this flag will be true and sysfs_remove_link() isn't called in
bcache_device_unlink().  Then when we attach this backing device again,
sysfs_create_link() will return EEXIST error in bcache_device_link().

So the fix is trival and we clear this flag in bcache_device_link().
Signed-off-by: NZheng Liu <wenqing.lz@taobao.com>
Tested-by: NJoshua Schmid <jschmid@suse.com>
Tested-by: NEric Wheeler <bcache@linux.ewheeler.net>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Tested-by: NEric Wheeler <bcache@linux.ewheeler.net>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

Subject :	[PATCH v2] bcache: fix a livelock in btree lock
Date :	Wed, 25 Feb 2015 20:32:09 +0800 (02/25/2015 04:32:09 AM)

This commit tries to fix a livelock in bcache.  This livelock might
happen when we causes a huge number of cache misses simultaneously.

When we get a cache miss, bcache will execute the following path.

->cached_dev_make_request()
  ->cached_dev_read()
    ->cached_lookup()
      ->bch->btree_map_keys()
        ->btree_root()  <------------------------
          ->bch_btree_map_keys_recurse()        |
            ->cache_lookup_fn()                 |
              ->cached_dev_cache_miss()         |
                ->bch_btree_insert_check_key() -|
                  [If btree->seq is not equal to seq + 1, we should return
                   EINTR and traverse btree again.]

In bch_btree_insert_check_key() function we first need to check upgrade
flag (op->lock == -1), and when this flag is true we need to release
read btree->lock and try to take write btree->lock.  During taking and
releasing this write lock, btree->seq will be monotone increased in
order to prevent other threads modify this in cache miss (see btree.h:74).
But if there are some cache misses caused by some requested, we could
meet a livelock because btree->seq is always changed by others.  Thus no
one can make progress.

This commit will try to take write btree->lock if it encounters a race
when we traverse btree.  Although it sacrifice the scalability but we
can ensure that only one can modify the btree.
Signed-off-by: NZheng Liu <wenqing.lz@taobao.com>
Tested-by: NJoshua Schmid <jschmid@suse.com>
Tested-by: NEric Wheeler <bcache@linux.ewheeler.net>
Cc: Joshua Schmid <jschmid@suse.com>
Cc: Zhu Yanhai <zhu.yanhai@gmail.com>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>

Commit 8182503d used monotonic time, but if the adapter is
using the seconds for logging entries, then we'll get duplicate
entries if the system is rebooted. Use real time instead.
Reported-by: NArnd Bergmann <arnd@arndb.de>
Fixes: 8182503d ("block: sx8.c: Replace timeval with ktime_t")
Signed-off-by: NJens Axboe <axboe@fb.com>

32-bit systems using 'struct timeval' will break in the year 2038,
in order to avoid that replace the code with more appropriate types.
This patch replaces timeval with 64 bit ktime_t which is y2038 safe.
Since st->timestamp is only interested in seconds, directly using
time64_t here. Function ktime_get_seconds is used since it uses
monotonic instead of real time and thus will not cause overflow.
Signed-off-by: NShraddha Barke <shraddha.6596@gmail.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

In case the lower level device size changed, but some other internal
details of the resize did not work out, drbd_determine_dev_size() would
try to restore the previous settings, trusting
drbd_md_set_sector_offsets() to "do the right thing", but overlooked
that this internally may set the meta data base offset based on device size.

This could end up with incomplete on-disk meta data layout change, and
ultimately lead to data corruption (if the failure was not noticed or
ignored by the operator, and other things go wrong as well).

Just remember all meta data related offsets/sizes,
and on error restore them all.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

During handshake communication, we also reconsider our device size,
using drbd_determine_dev_size(). Just in case we need to change the
offsets or layout of our on-disk metadata, we lock out application
and other meta data IO, and wait for the activity log to be "idle"
(no more referenced extents).

If this handshake happens just after a connection loss, with a fencing
policy of "resource-and-stonith", we have frozen IO.

If, additionally, the activity log was "starving" (too many incoming
random writes at that point in time), it won't become idle, ever,
because of the frozen IO, and this would be a lockup of the receiver
thread, and consquentially of DRBD.

Previous logic (re-)initialized with a special "empty" transaction
block, which required the activity log to fully drain first.

Instead, write out some standard activity log transactions.
Using lc_try_lock_for_transaction() instead of lc_try_lock() does not
care about pending activity log references, avoiding the potential
deadlock.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

To be able to "force out" an activity log transaction,
even if there are no pending updates.

This will be used to relocate the on-disk activity log,
if the on-disk offsets have to be changed,
without the need to empty the activity log first.

While at it, move the definition,
so we can drop the forward declaration of a static helper.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Avoid to prematurely resume application IO: don't set/clear a single
bit, but inc/dec an atomic counter.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Don't remember a DRBD request as ack_pending, if it is not.

In protocol A, we usually clear RQ_NET_PENDING at the same time we set
RQ_NET_SENT, so when deciding to remember it as ack_pending,
mod_rq_state needs to look at the current request state,
not at the previous state before the current modification was applied.

This should prevent advance_conn_req_ack_pending() from walking the full
transfer log just to find NULL in protocol A, which would cause serious
performance degradation with many "in-flight" requests, e.g. when
working via DRBD-proxy, or with a huge bandwidth-delay product.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

new_disk_conf could be leaked if the follow on checks fail,
so make sure to free it on error if it was not assigned yet.

Found with smatch.
Signed-off-by: NOleg Drokin <green@linuxhacker.ru>
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Disconnect should wait for pending bitmap IO.
But if that bitmap IO is not happening, because it is waiting for
pending application IO, and there is no progress, because the fencing
policy suspended application IO because of the disconnect,
then we deadlock.

The bitmap writeout in this case does not care for concurrent
application IO, so there is no point waiting for it.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Fix the semantic of lc_seq_printf. Currently, it always returns 0 and
the return value is unused, therefore, convert the return type to void.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

lsblk should be able to pick up stacking device driver relations
involving DRBD conveniently.

Even though upstream kernel since 2011 says
	"DON'T USE THIS UNLESS YOU'RE ALREADY USING IT."
a new user has been added since (bcache),
which sets the precedences for us to use it as well.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

We cannot possibly support SECDISCARD, even if all backend devices would
support it: if our peer is currently unreachable, some instance of the
data may obviously still be recoverable.

We did not set discard_granularity at all.  We don't really care (yet),
we only pass them on, so for now, set our granularity to one sector.
blkdev_stack_limits() takes care of the rest.

If we decide we cannot support discards,
not only clear the (not user visible) QUEUE_FLAG_DISCARD,
but set both (user visible) discard_granularity and max_discard_sectors
to zero, to avoid confusion with e.g. lsblk -D.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

When accessing out meta data area on disk, we double check the
plausibility of the requested sector offsets, and are very noisy about
it if they look suspicious.

During initial read of our "superblock", for "external" meta data,
this triggered because the range estimate returned by
drbd_md_last_sector() was still wrong.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Suggested by Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Apparently we now implicitly get definitions for BITS_PER_PAGE and
BITS_PER_PAGE_MASK from the pid_namespace.h

Instead of renaming our defines, I chose to define only if not yet
defined, but to double check the value if already defined.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Since kernel 3.3, we can use snprintf-style arguments
to create a workqueue.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

The effective data generation ID may be interesting for debugging
purposes of scenarios involving diskless states.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

In a multiple error scenario, we may end up with a "frozen" Primary,
that has no access to any data (no local disk, no replication link).

If we then resume-io, we try to generate a new data generation id,
which will fail if there is no longer a local disk.

Double check for available local data,
which prevents the NULL pointer deref.

If we are diskless, turn the resume-io in this situation
into the first stage of a "force down", by bumping the "effective" data
gen id, which will prevent later attach or connect to the former data
set without first being demoted (deconfigured).
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

The intention is to reduce CPU utilization. Recent measurements
unveiled that the current performance bottleneck is CPU utilization
on the receiving node. The asender thread became CPU limited.

One of the main points is to eliminate the idr_for_each_entry() loop
from the sending acks code path.

One exception in that is sending back ping_acks. These stay
in the ack-receiver thread. Otherwise the logic becomes too
complicated for no added value.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

This prepares the next patch where the sending on the meta (or
control) socket is moved to a dedicated workqueue.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

A D_FAILED disk transitions as quickly as possible to
D_DISKLESS. But in the "unresponsive local disk" case,
there remains a time window where a administrative detach command could
find the disk already failed, but some internal meta data IO against the
unresponsive local disk still pending.

In that case, drbd_md_get_buffer() will return NULL.
Don't unconditionally call drbd_md_put_buffer(), or it will cause
refcount imbalance, and prevent any further re-attach on this volume
(until it is deleted and re-created).
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

The recent (not yet released) backport of the extended state broadcasts
to support the "events2" subcommand of drbdsetup had some glitches.

remember_old_state() would first count all connections with a
net_conf != NULL, then allocate a suitable array, then populate that
array with all connections found to have net_conf != NULL.

This races with the state change to C_STANDALONE,
and the NULL assignment there.

remember_new_state() then iterates over said connection array,
assuming that it would be fully populated.

But rcu_lock() just makes sure the thing some pointer points to,
if any, won't go away. It does not make the pointer itself immutable.

In fact there is no need to "filter" connections based on whether or not
they have a currently valid configuration.  Just record them always, if
they don't have a config, that's fine, there will be no change then.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

Don't blame the peer for being unresponsive,
if we did not even ask the question yet.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

The only way to make DRBD intentionally call panic is to
set a disk timeout, have that trigger, "abort" some request and complete
to upper layers, then have the backend IO subsystem later complete these
requests successfully regardless.

As the attached IO pages have been recycled for other purposes
meanwhile, this will cause unexpected random memory changes.
To prevent corruption, we rather panic in that case.

Make it obvious from stack traces that this was the case by introducing
drbd_panic_after_delayed_completion_of_aborted_request().
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@fb.com>