forked from Minki/linux
mainlining shenanigans
0ee223b2e1
A long time ago the unfortunate decision was taken to add a self-deletion
attribute to the sysfs SCSI device directory. That decision was unfortunate
because self-deletion is really tricky. We can't drop that attribute
because widely used user space software depends on it, namely the
rescan-scsi-bus.sh script. Hence this patch that avoids that writing into
that attribute triggers a deadlock. See also commit 7973cbd9fbd9 ("[PATCH]
add sysfs attributes to scan and delete scsi_devices").
This patch avoids that self-removal triggers the following deadlock:
======================================================
WARNING: possible circular locking dependency detected
4.18.0-rc2-dbg+ #5 Not tainted
------------------------------------------------------
modprobe/6539 is trying to acquire lock:
000000008323c4cd (kn->count#202){++++}, at: kernfs_remove_by_name_ns+0x45/0x90
but task is already holding lock:
00000000a6ec2c69 (&shost->scan_mutex){+.+.}, at: scsi_remove_host+0x21/0x150 [scsi_mod]
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&shost->scan_mutex){+.+.}:
__mutex_lock+0xfe/0xc70
mutex_lock_nested+0x1b/0x20
scsi_remove_device+0x26/0x40 [scsi_mod]
sdev_store_delete+0x27/0x30 [scsi_mod]
dev_attr_store+0x3e/0x50
sysfs_kf_write+0x87/0xa0
kernfs_fop_write+0x190/0x230
__vfs_write+0xd2/0x3b0
vfs_write+0x101/0x270
ksys_write+0xab/0x120
__x64_sys_write+0x43/0x50
do_syscall_64+0x77/0x230
entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #0 (kn->count#202){++++}:
lock_acquire+0xd2/0x260
__kernfs_remove+0x424/0x4a0
kernfs_remove_by_name_ns+0x45/0x90
remove_files.isra.1+0x3a/0x90
sysfs_remove_group+0x5c/0xc0
sysfs_remove_groups+0x39/0x60
device_remove_attrs+0x82/0xb0
device_del+0x251/0x580
__scsi_remove_device+0x19f/0x1d0 [scsi_mod]
scsi_forget_host+0x37/0xb0 [scsi_mod]
scsi_remove_host+0x9b/0x150 [scsi_mod]
sdebug_driver_remove+0x4b/0x150 [scsi_debug]
device_release_driver_internal+0x241/0x360
device_release_driver+0x12/0x20
bus_remove_device+0x1bc/0x290
device_del+0x259/0x580
device_unregister+0x1a/0x70
sdebug_remove_adapter+0x8b/0xf0 [scsi_debug]
scsi_debug_exit+0x76/0xe8 [scsi_debug]
__x64_sys_delete_module+0x1c1/0x280
do_syscall_64+0x77/0x230
entry_SYSCALL_64_after_hwframe+0x49/0xbe
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&shost->scan_mutex);
lock(kn->count#202);
lock(&shost->scan_mutex);
lock(kn->count#202);
*** DEADLOCK ***
2 locks held by modprobe/6539:
#0: 00000000efaf9298 (&dev->mutex){....}, at: device_release_driver_internal+0x68/0x360
#1: 00000000a6ec2c69 (&shost->scan_mutex){+.+.}, at: scsi_remove_host+0x21/0x150 [scsi_mod]
stack backtrace:
CPU: 10 PID: 6539 Comm: modprobe Not tainted 4.18.0-rc2-dbg+ #5
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
Call Trace:
dump_stack+0xa4/0xf5
print_circular_bug.isra.34+0x213/0x221
__lock_acquire+0x1a7e/0x1b50
lock_acquire+0xd2/0x260
__kernfs_remove+0x424/0x4a0
kernfs_remove_by_name_ns+0x45/0x90
remove_files.isra.1+0x3a/0x90
sysfs_remove_group+0x5c/0xc0
sysfs_remove_groups+0x39/0x60
device_remove_attrs+0x82/0xb0
device_del+0x251/0x580
__scsi_remove_device+0x19f/0x1d0 [scsi_mod]
scsi_forget_host+0x37/0xb0 [scsi_mod]
scsi_remove_host+0x9b/0x150 [scsi_mod]
sdebug_driver_remove+0x4b/0x150 [scsi_debug]
device_release_driver_internal+0x241/0x360
device_release_driver+0x12/0x20
bus_remove_device+0x1bc/0x290
device_del+0x259/0x580
device_unregister+0x1a/0x70
sdebug_remove_adapter+0x8b/0xf0 [scsi_debug]
scsi_debug_exit+0x76/0xe8 [scsi_debug]
__x64_sys_delete_module+0x1c1/0x280
do_syscall_64+0x77/0x230
entry_SYSCALL_64_after_hwframe+0x49/0xbe
See also https://www.mail-archive.com/linux-scsi@vger.kernel.org/msg54525.html.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.