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scsi: target: Avoid that EXTENDED COPY commands trigger lock inversion

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The approach for adding a device to the devices_idr data structure and for
removing it is as follows:

* &dev->dev_group.cg_item is initialized before a device is added to
  devices_idr.

* If the reference count of a device drops to zero then
  target_free_device() removes the device from devices_idr.

* All devices_idr manipulations are protected by device_mutex.

This means that increasing the reference count of a device is sufficient to
prevent removal from devices_idr and also that it is safe access
dev_group.cg_item for any device that is referenced by devices_idr. Use
this to modify target_find_device() and target_for_each_device() such that
these functions no longer introduce a dependency between device_mutex and
the configfs root inode mutex.

Note: it is safe to pass a NULL pointer to config_item_put() and also to
config_item_get_unless_zero().

This patch prevents that lockdep reports the following complaint:

======================================================
WARNING: possible circular locking dependency detected
4.12.0-rc1-dbg+ #1 Not tainted
------------------------------------------------------
rmdir/12053 is trying to acquire lock:
 (device_mutex#2){+.+.+.}, at: [<ffffffffa010afce>]
target_free_device+0xae/0xf0 [target_core_mod]

but task is already holding lock:
 (&sb->s_type->i_mutex_key#14){++++++}, at: [<ffffffff811c5c30>]
vfs_rmdir+0x50/0x140

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&sb->s_type->i_mutex_key#14){++++++}:
       lock_acquire+0x59/0x80
       down_write+0x36/0x70
       configfs_depend_item+0x3a/0xb0 [configfs]
       target_depend_item+0x13/0x20 [target_core_mod]
       target_xcopy_locate_se_dev_e4_iter+0x87/0x100 [target_core_mod]
       target_devices_idr_iter+0x16/0x20 [target_core_mod]
       idr_for_each+0x39/0xc0
       target_for_each_device+0x36/0x50 [target_core_mod]
       target_xcopy_locate_se_dev_e4+0x28/0x80 [target_core_mod]
       target_xcopy_do_work+0x2e9/0xdd0 [target_core_mod]
       process_one_work+0x1ca/0x3f0
       worker_thread+0x49/0x3b0
       kthread+0x109/0x140
       ret_from_fork+0x31/0x40

-> #0 (device_mutex#2){+.+.+.}:
       __lock_acquire+0x101f/0x11d0
       lock_acquire+0x59/0x80
       __mutex_lock+0x7e/0x950
       mutex_lock_nested+0x16/0x20
       target_free_device+0xae/0xf0 [target_core_mod]
       target_core_dev_release+0x10/0x20 [target_core_mod]
       config_item_put+0x6e/0xb0 [configfs]
       configfs_rmdir+0x1a6/0x300 [configfs]
       vfs_rmdir+0xb7/0x140
       do_rmdir+0x1f4/0x200
       SyS_rmdir+0x11/0x20
       entry_SYSCALL_64_fastpath+0x23/0xc2

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sb->s_type->i_mutex_key#14);
                               lock(device_mutex#2);
                               lock(&sb->s_type->i_mutex_key#14);
  lock(device_mutex#2);

 *** DEADLOCK ***

3 locks held by rmdir/12053:
 #0:  (sb_writers#10){.+.+.+}, at: [<ffffffff811e223f>]
mnt_want_write+0x1f/0x50
 #1:  (&sb->s_type->i_mutex_key#14/1){+.+.+.}, at: [<ffffffff811cb97e>]
do_rmdir+0x15e/0x200
 #2:  (&sb->s_type->i_mutex_key#14){++++++}, at: [<ffffffff811c5c30>]
vfs_rmdir+0x50/0x140

stack backtrace:
CPU: 3 PID: 12053 Comm: rmdir Not tainted 4.12.0-rc1-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.0.0-prebuilt.qemu-project.org 04/01/2014
Call Trace:
 dump_stack+0x86/0xcf
 print_circular_bug+0x1c7/0x220
 __lock_acquire+0x101f/0x11d0
 lock_acquire+0x59/0x80
 __mutex_lock+0x7e/0x950
 mutex_lock_nested+0x16/0x20
 target_free_device+0xae/0xf0 [target_core_mod]
 target_core_dev_release+0x10/0x20 [target_core_mod]
 config_item_put+0x6e/0xb0 [configfs]
 configfs_rmdir+0x1a6/0x300 [configfs]
 vfs_rmdir+0xb7/0x140
 do_rmdir+0x1f4/0x200
 SyS_rmdir+0x11/0x20
 entry_SYSCALL_64_fastpath+0x23/0xc2

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
[Rebased to handle conflict withe target_find_device removal]
Signed-off-by: Mike Christie <mchristi@redhat.com>

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Bart Van Assche 2018-06-28 13:48:57 -05:00 committed by Martin K. Petersen
parent 6f3bf5a2fa
commit 36d4cb460b
1 changed files with 17 additions and 5 deletions
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22
drivers/target/target_core_device.c
View File

@ -880,14 +880,20 @@ sector_t target_to_linux_sector(struct se_device *dev, sector_t lb)
EXPORT_SYMBOL(target_to_linux_sector);
struct devices_idr_iter {
struct config_item *prev_item;
int (*fn)(struct se_device *dev, void *data);
void *data;
};
static int target_devices_idr_iter(int id, void *p, void *data)
__must_hold(&device_mutex)
{
struct devices_idr_iter *iter = data;
struct se_device *dev = p;
int ret;
config_item_put(iter->prev_item);
iter->prev_item = NULL;
/*
* We add the device early to the idr, so it can be used
@ -898,7 +904,15 @@ static int target_devices_idr_iter(int id, void *p, void *data)
if (!(dev->dev_flags & DF_CONFIGURED))
return 0;
return iter->fn(dev, iter->data);
iter->prev_item = config_item_get_unless_zero(&dev->dev_group.cg_item);
if (!iter->prev_item)
return 0;
mutex_unlock(&device_mutex);
ret = iter->fn(dev, iter->data);
mutex_lock(&device_mutex);
return ret;
}
/**
@ -912,15 +926,13 @@ static int target_devices_idr_iter(int id, void *p, void *data)
int target_for_each_device(int (*fn)(struct se_device *dev, void *data),
void *data)
{
struct devices_idr_iter iter;
struct devices_idr_iter iter = { .fn = fn, .data = data };
int ret;
iter.fn = fn;
iter.data = data;
mutex_lock(&device_mutex);
ret = idr_for_each(&devices_idr, target_devices_idr_iter, &iter);
mutex_unlock(&device_mutex);
config_item_put(iter.prev_item);
return ret;
}