tcmu: fix crash when removing the tcmu device

Before the nl REMOVE msg has been sent to the userspace, the ring's
and other resources have been released, but the userspace maybe still
using them. An

tcmu: fix crash when removing the tcmu device

Before the nl REMOVE msg has been sent to the userspace, the ring's
and other resources have been released, but the userspace maybe still
using them. And then we can see the crash messages like:

ring broken, not handling completions
BUG: unable to handle kernel paging request at ffffffffffffffd0
IP: tcmu_handle_completions+0x134/0x2f0 [target_core_user]
PGD 11bdc0c067
P4D 11bdc0c067
PUD 11bdc0e067
PMD 0

Oops: 0000 [#1] SMP
cmd_id not found, ring is broken
RIP: 0010:tcmu_handle_completions+0x134/0x2f0 [target_core_user]
RSP: 0018:ffffb8a2d8983d88 EFLAGS: 00010296
RAX: 0000000000000000 RBX: ffffb8a2aaa4e000 RCX: 00000000ffffffff
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000220
R10: 0000000076c71401 R11: ffff8d2e76c713f0 R12: ffffb8a2aad56bc0
R13: 000000000000001c R14: ffff8d2e32c90000 R15: ffff8d2e76c713f0
FS: 00007f411ffff700(0000) GS:ffff8d1e7fdc0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd0 CR3: 0000001027070000 CR4:
00000000001406e0
Call Trace:
? tcmu_irqcontrol+0x2a/0x40 [target_core_user]
? uio_write+0x7b/0xc0 [uio]
? __vfs_write+0x37/0x150
? __getnstimeofday64+0x3b/0xd0
? vfs_write+0xb2/0x1b0
? syscall_trace_enter+0x1d0/0x2b0
? SyS_write+0x55/0xc0
? do_syscall_64+0x67/0x150
? entry_SYSCALL64_slow_path+0x25/0x25
Code: 41 5d 41 5e 41 5f 5d c3 83 f8 01 0f 85 cf 01 00
00 48 8b 7d d0 e8 dd 5c 1d f3 41 0f b7 74 24 04 48 8b
7d c8 31 d2 e8 5c c7 1b f3 <48> 8b 7d d0 49 89 c7 c6 07
00 0f 1f 40 00 4d 85 ff 0f 84 82 01 RIP:
tcmu_handle_completions+0x134/0x2f0 [target_core_user]
RSP: ffffb8a2d8983d88
CR2: ffffffffffffffd0

And the crash also could happen in tcmu_page_fault and other places.

Signed-off-by: Zhang Zhuoyu <zhangzhuoyu@cmss.chinamobile.com>
Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()

Please do not apply this to mainline directly, instead please re-run the
coccinelle script sh

locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()

Please do not apply this to mainline directly, instead please re-run the
coccinelle script shown below and apply its output.

For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't harmful, and changing them results in
churn.

However, for some features, the read/write distinction is critical to
correct operation. To distinguish these cases, separate read/write
accessors must be used. This patch migrates (most) remaining
ACCESS_ONCE() instances to {READ,WRITE}_ONCE(), using the following
coccinelle script:

----
// Convert trivial ACCESS_ONCE() uses to equivalent READ_ONCE() and
// WRITE_ONCE()

// $ make coccicheck COCCI=/home/mark/once.cocci SPFLAGS="--include-headers" MODE=patch

virtual patch

@ depends on patch @
expression E1, E2;
@@

- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)

@ depends on patch @
expression E;
@@

- ACCESS_ONCE(E)
+ READ_ONCE(E)
----

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-19-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

show more ...

tcmu: free old string on reconfig

On initial tcmu_configure_device call the info->name would
have already been allocated and set, so on the second call
make sure to free it first.

Reported-by: Mike

tcmu: free old string on reconfig

On initial tcmu_configure_device call the info->name would
have already been allocated and set, so on the second call
make sure to free it first.

Reported-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Fix possible to/from address overflow when doing the memcpy

For most case the sg->length equals to PAGE_SIZE, so this bug won't
be triggered. Otherwise this will crash the kernel, for example

tcmu: Fix possible to/from address overflow when doing the memcpy

For most case the sg->length equals to PAGE_SIZE, so this bug won't
be triggered. Otherwise this will crash the kernel, for example when
all segments' sg->length equal to 1K.

Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: clean up the code and with one small fix

Remove useless blank line and code and at the same time add one error
path to catch the errors.

Reviewed-by: Mike Christie <mchristi@redhat.com>
Signe

tcmu: clean up the code and with one small fix

Remove useless blank line and code and at the same time add one error
path to catch the errors.

Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Fix possbile memory leak / OOPs when recalculating cmd base size

For all the entries allocated from the ring cmd area, the memory is
something like the stack memory, which will always reserve

tcmu: Fix possbile memory leak / OOPs when recalculating cmd base size

For all the entries allocated from the ring cmd area, the memory is
something like the stack memory, which will always reserve the old
data, so the entry->req.iov_bidi_cnt maybe none zero.

On some environments, the crash could be reproduce very easy and some
not. The following is the crash core trace as reported by Damien:

[ 240.143969] CPU: 0 PID: 1285 Comm: iscsi_trx Not tainted 4.12.0-rc1+ #3
[ 240.150607] Hardware name: ASUS All Series/H87-PRO, BIOS 2104 10/28/2014
[ 240.157331] task: ffff8807de4f5800 task.stack: ffffc900047dc000
[ 240.163270] RIP: 0010:memcpy_erms+0x6/0x10
[ 240.167377] RSP: 0018:ffffc900047dfc68 EFLAGS: 00010202
[ 240.172621] RAX: ffffc9065db85540 RBX: ffff8807f7980000 RCX: 0000000000000010
[ 240.179771] RDX: 0000000000000010 RSI: ffff8807de574fe0 RDI: ffffc9065db85540
[ 240.186930] RBP: ffffc900047dfd30 R08: ffff8807de41b000 R09: 0000000000000000
[ 240.194088] R10: 0000000000000040 R11: ffff8807e9b726f0 R12: 00000006565726b0
[ 240.201246] R13: ffffc90007612ea0 R14: 000000065657d540 R15: 0000000000000000
[ 240.208397] FS: 0000000000000000(0000) GS:ffff88081fa00000(0000) knlGS:0000000000000000
[ 240.216510] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 240.222280] CR2: ffffc9065db85540 CR3: 0000000001c0f000 CR4: 00000000001406f0
[ 240.229430] Call Trace:
[ 240.231887] ? tcmu_queue_cmd+0x83c/0xa80
[ 240.235916] ? target_check_reservation+0xcd/0x6f0
[ 240.240725] __target_execute_cmd+0x27/0xa0
[ 240.244918] target_execute_cmd+0x232/0x2c0
[ 240.249124] ? __local_bh_enable_ip+0x64/0xa0
[ 240.253499] iscsit_execute_cmd+0x20d/0x270
[ 240.257693] iscsit_sequence_cmd+0x110/0x190
[ 240.261985] iscsit_get_rx_pdu+0x360/0xc80
[ 240.267565] ? iscsi_target_rx_thread+0x54/0xd0
[ 240.273571] iscsi_target_rx_thread+0x9a/0xd0
[ 240.279413] kthread+0x113/0x150
[ 240.284120] ? iscsi_target_tx_thread+0x1e0/0x1e0
[ 240.290297] ? kthread_create_on_node+0x40/0x40
[ 240.296297] ret_from_fork+0x2e/0x40
[ 240.301332] Code: 90 90 90 90 90 eb 1e 0f 1f 00 48 89 f8 48 89 d1 48
c1 e9 03 83 e2 07 f3 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48
89 d1 <f3> a4 c3 0f 1f 80 00 00 00 00 48 89 f8 48 83 fa 20 72 7e 40 38
[ 240.321751] RIP: memcpy_erms+0x6/0x10 RSP: ffffc900047dfc68
[ 240.328838] CR2: ffffc9065db85540
[ 240.333667] ---[ end trace b7e5354cfb54d08b ]---

To fix this, just memset all the entry memory before using it, and
also to be more readable we adjust the bidi code.

Fixed: fe25cc34795(tcmu: Recalculate the tcmu_cmd size to save cmd area
memories)
Reported-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Tested-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reported-by: Damien Le Moal <damien.lemoal@wdc.com>
Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Cc: <stable@vger.kernel.org> # 4.12+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Fix dev_config_store

Currently when there is a reconfig, the uio_info->name
does not get updated to reflect the change in the dev_config
name change.

On restart tcmu-runner there will be a mi

tcmu: Fix dev_config_store

Currently when there is a reconfig, the uio_info->name
does not get updated to reflect the change in the dev_config
name change.

On restart tcmu-runner there will be a mismatch between
the dev_config string in uio and the tcmu structure that contains
the string. When this occurs it'll reload the one in uio
and you lose the reconfigured device path.

v2: Created a helper function for the updating of uio_info

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: fix sense handling during completion

We were just copying the sense to the cmd sense_buffer and
did not implement a transport_complete or set the
SCF_TRANSPORT_TASK_SENSE, so the sense was ign

tcmu: fix sense handling during completion

We were just copying the sense to the cmd sense_buffer and
did not implement a transport_complete or set the
SCF_TRANSPORT_TASK_SENSE, so the sense was ignored.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Fix flushing cmd entry dcache page

When feeding the tcmu's cmd ring, we need to flush the dcache page
for the cmd entry to make sure these kernel stores are visible to
user space mappings of t

tcmu: Fix flushing cmd entry dcache page

When feeding the tcmu's cmd ring, we need to flush the dcache page
for the cmd entry to make sure these kernel stores are visible to
user space mappings of that page.

For the none PAD cmd entry, this will be flushed at the end of the
tcmu_queue_cmd_ring().

Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: fix multiple uio open/close sequences

If the uio device is open and closed multiple times, the
kref count will be off due to tcmu_release getting called
multiple times for each close. This pat

tcmu: fix multiple uio open/close sequences

If the uio device is open and closed multiple times, the
kref count will be off due to tcmu_release getting called
multiple times for each close. This patch integrates
Wenji Tang's patch to add a kref_get on open that now
matches the kref_put done on tcmu_release and adds
a kref_put in tcmu_destroy_device to match the kref_get
done in succesful tcmu_configure_device calls.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Cc: Wenji Tang <tang.wenji@zte.com.cn>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: drop configured check in destroy

destroy_device is only called if we have successfully run
configure_device, so drop the duplicate tcmu_dev_configured check.

Signed-off-by: Mike Christie <mch

tcmu: drop configured check in destroy

destroy_device is only called if we have successfully run
configure_device, so drop the duplicate tcmu_dev_configured check.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: perfom device add, del and reconfig synchronously

This makes the device add, del reconfig operations sync. It fixes
the issue where for add and reconfig, we do not know if userspace
successful

tcmu: perfom device add, del and reconfig synchronously

This makes the device add, del reconfig operations sync. It fixes
the issue where for add and reconfig, we do not know if userspace
successfully completely the operation, so we leave invalid kernel
structs or report incorrect status for the config/reconfig operations.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

target: break up free_device callback

With this patch free_device is now used to free what is allocated in the
alloc_device callback and destroy_device tears down the resources that are
setup in the

target: break up free_device callback

With this patch free_device is now used to free what is allocated in the
alloc_device callback and destroy_device tears down the resources that are
setup in the configure_device callback.

This patch will be needed in the next patch where tcmu needs
to be able to look up the device in the destroy callback.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: reconfigure netlink attr changes

1. TCMU_ATTR_TYPE is too generic when it describes only the
reconfiguration type, so rename to TCMU_ATTR_RECONFIG_TYPE.

2. Only return the reconfig type when

tcmu: reconfigure netlink attr changes

1. TCMU_ATTR_TYPE is too generic when it describes only the
reconfiguration type, so rename to TCMU_ATTR_RECONFIG_TYPE.

2. Only return the reconfig type when it is a
TCMU_CMD_RECONFIG_DEVICE command.

3. CONFIG_* type is not needed. We can pass the value along with an
ATTR to userspace, so it does not need to read sysfs/configfs.

4. Fix leak in tcmu_dev_path_store and rename to dev_config to
reflect it is more than just a path that can be changed.

6. Don't update kernel struct value if netlink sending fails.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: "Bryant G. Ly" <bryantly@linux.vnet.ibm.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: make array tcmu_attrib_attrs static const

The array tcmu_attrib_attrs does not need to be in global scope, so make
it static.

Cleans up sparse warning:
"symbol 'tcmu_attrib_attrs' was not dec

tcmu: make array tcmu_attrib_attrs static const

The array tcmu_attrib_attrs does not need to be in global scope, so make
it static.

Cleans up sparse warning:
"symbol 'tcmu_attrib_attrs' was not declared. Should it be static?"

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Fix module removal due to stuck unmap_thread thread again

Because the unmap code just after the schdule() returned may take
a long time and if the kthread_stop() is fired just when in this
rou

tcmu: Fix module removal due to stuck unmap_thread thread again

Because the unmap code just after the schdule() returned may take
a long time and if the kthread_stop() is fired just when in this
routine, the module removal maybe stuck too.

Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Add Type of reconfig into netlink

This patch adds more info about the attribute being changed,
so that usersapce can easily figure out what is happening.

Signed-off-by: Bryant G. Ly <bryantly

tcmu: Add Type of reconfig into netlink

This patch adds more info about the attribute being changed,
so that usersapce can easily figure out what is happening.

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reviewed-By: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Make dev_config configurable

This allows for userspace to change the device path after
it has been created. Thus giving the user the ability to change
the path. The use case for this is to all

tcmu: Make dev_config configurable

This allows for userspace to change the device path after
it has been created. Thus giving the user the ability to change
the path. The use case for this is to allow for virtual optical
to have media change.

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reviewed-By: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Make dev_size configurable via userspace

Allow tcmu backstores to be able to set the device size
after it has been configured via set attribute.

Part of support in userspace to support certai

tcmu: Make dev_size configurable via userspace

Allow tcmu backstores to be able to set the device size
after it has been configured via set attribute.

Part of support in userspace to support certain backstores
changing device size.

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reviewed-By: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Add netlink for device reconfiguration

This gives tcmu the ability to handle events that can cause
reconfiguration, such as resize, path changes, write_cache, etc...

Signed-off-by: Bryant G.

tcmu: Add netlink for device reconfiguration

This gives tcmu the ability to handle events that can cause
reconfiguration, such as resize, path changes, write_cache, etc...

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reviewed-By: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Support emulate_write_cache

This will enable the toggling of write_cache in tcmu through targetcli-fb

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reviewed-By: Mike Christie <mch

tcmu: Support emulate_write_cache

This will enable the toggling of write_cache in tcmu through targetcli-fb

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Reviewed-By: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: fix crash during device removal

We currently do

tcmu_free_device ->tcmu_netlink_event(TCMU_CMD_REMOVED_DEVICE) ->
uio_unregister_device -> kfree(tcmu_dev).

The problem is that the kernel doe

tcmu: fix crash during device removal

We currently do

tcmu_free_device ->tcmu_netlink_event(TCMU_CMD_REMOVED_DEVICE) ->
uio_unregister_device -> kfree(tcmu_dev).

The problem is that the kernel does not wait for userspace to
do the close() on the uio device before freeing the tcmu_dev.
We can then hit a race where the kernel frees the tcmu_dev before
userspace does close() and so when close() -> release -> tcmu_release
is done, we try to access a freed tcmu_dev.

This patch made over the target-pending master branch moves the freeing
of the tcmu_dev to when the last reference has been dropped.

This also fixes a leak where if tcmu_configure_device was not called on a
device we did not free udev->name which was allocated at tcmu_alloc_device time.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: fix module removal due to stuck thread

We need to do a kthread_should_stop to check when kthread_stop has been
called.

This was a regression added in

b6df4b79a5514a9c6c53533436704129ef45bf76

tcmu: fix module removal due to stuck thread

We need to do a kthread_should_stop to check when kthread_stop has been
called.

This was a regression added in

b6df4b79a5514a9c6c53533436704129ef45bf76
tcmu: Add global data block pool support

so not sure if you wanted to merge it in with that patch or what.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Recalculate the tcmu_cmd size to save cmd area memories

For the "struct tcmu_cmd_entry" in cmd area, the minimum size
will be sizeof(struct tcmu_cmd_entry) == 112 Bytes. And it could
fill abou

tcmu: Recalculate the tcmu_cmd size to save cmd area memories

For the "struct tcmu_cmd_entry" in cmd area, the minimum size
will be sizeof(struct tcmu_cmd_entry) == 112 Bytes. And it could
fill about (sizeof(struct rsp) - sizeof(struct req)) /
sizeof(struct iovec) == 68 / 16 ~= 4 data regions(iov[4]) by
default.

For most tcmu_cmds, the data block indexes allocated from the
data area will be continuous. And for the continuous blocks they
will be merged into the same region using only one iovec. For
the current code, it will always allocates the same number of
iovecs with blocks for each tcmu_cmd, and it will wastes much
memories.

For example, when the block size is 4K and the DATA_OUT buffer
size is 64K, and the regions needed is less than 5(on my
environment is almost 99.7%). The current code will allocate
about 16 iovecs, and there will be (16 - 4) * sizeof(struct
iovec) = 192 Bytes cmd area memories wasted.

Here adds two helpers to calculate the base size and full size
of the tcmu_cmd. And will recalculate them again when it make sure
how many iovs is needed before insert it to cmd area.

Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Acked-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

show more ...

tcmu: Add global data block pool support

For each target there will be one ring, when the target number
grows larger and larger, it could eventually runs out of the
system memories.

In this patch f

tcmu: Add global data block pool support

For each target there will be one ring, when the target number
grows larger and larger, it could eventually runs out of the
system memories.

In this patch for each target ring, currently for the cmd area
the size will be fixed to 8MB and for the data area the size
will grow from 0 to max 256K * PAGE_SIZE(1G for 4K page size).

For all the targets' data areas, they will get empty blocks
from the "global data block pool", which has limited to 512K *
PAGE_SIZE(2G for 4K page size) for now.

When the "global data block pool" has been used up, then any
target could wake up the unmap thread routine to shrink other
targets' data area memories. And the unmap thread routine will
always try to truncate the ring vma from the last using block
offset.

When user space has touched the data blocks out of tcmu_cmd
iov[], the tcmu_page_fault() will try to return one zeroed blocks.

Here we move the timeout's tcmu_handle_completions() into unmap
thread routine, that's to say when the timeout fired, it will
only do the tcmu_check_expired_cmd() and then wake up the unmap
thread to do the completions() and then try to shrink its idle
memories. Then the cmdr_lock could be a mutex and could simplify
this patch because the unmap_mapping_range() or zap_* may go to
sleep.

Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Signed-off-by: Jianfei Hu <hujianfei@cmss.chinamobile.com>
Acked-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

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