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Filename Latest commit message Latest commit date
Michael Schmitz 5213cc01d0 m68k: Fix spinlock race in kernel thread creation
[ Upstream commit da89ce46f02470ef08f0f580755d14d547da59ed ]

Context switching does take care to retain the correct lock owner across
the switch from 'prev' to 'next' tasks.  This does rely on interrupts
remaining disabled for the entire duration of the switch.

This condition is guaranteed for normal process creation and context
switching between already running processes, because both 'prev' and
'next' already have interrupts disabled in their saved copies of the
status register.

The situation is different for newly created kernel threads.  The status
register is set to PS_S in copy_thread(), which does leave the IPL at 0.
Upon restoring the 'next' thread's status register in switch_to() aka
resume(), interrupts then become enabled prematurely.  resume() then
returns via ret_from_kernel_thread() and schedule_tail() where run queue
lock is released (see finish_task_switch() and finish_lock_switch()).

A timer interrupt calling scheduler_tick() before the lock is released
in finish_task_switch() will find the lock already taken, with the
current task as lock owner.  This causes a spinlock recursion warning as
reported by Guenter Roeck.

As far as I can ascertain, this race has been opened in commit
533e6903be ("m68k: split ret_from_fork(), simplify kernel_thread()")
but I haven't done a detailed study of kernel history so it may well
predate that commit.

Interrupts cannot be disabled in the saved status register copy for
kernel threads (init will complain about interrupts disabled when
finally starting user space).  Disable interrupts temporarily when
switching the tasks' register sets in resume().

Note that a simple oriw 0x700,%sr after restoring sr is not enough here
- this leaves enough of a race for the 'spinlock recursion' warning to
still be observed.

Tested on ARAnyM and qemu (Quadra 800 emulation).

Fixes: 533e6903be ("m68k: split ret_from_fork(), simplify kernel_thread()")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/all/07811b26-677c-4d05-aeb4-996cd880b789@roeck-us.net
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20240411033631.16335-1-schmitzmic@gmail.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2024-06-16 13:28:37 +02:00
arch m68k: Fix spinlock race in kernel thread creation 2024-06-16 13:28:37 +02:00
block block: prevent division by zero in blk_rq_stat_sum() 2024-04-13 12:51:38 +02:00
certs
crypto Revert "crypto: api - Disallow identical driver names" 2024-05-02 16:18:35 +02:00
Documentation ASoC: dt-bindings: rt5645: add cbj sleeve gpio property 2024-06-16 13:28:31 +02:00
drivers net: usb: sr9700: stop lying about skb->truesize 2024-06-16 13:28:37 +02:00
fs jffs2: prevent xattr node from overflowing the eraseblock 2024-06-16 13:28:33 +02:00
include xfrm: Preserve vlan tags for transport mode software GRO 2024-05-17 11:43:53 +02:00
init
ipc
kernel ring-buffer: Fix a race between readers and resize checks 2024-06-16 13:28:30 +02:00
lib dyndbg: fix old BUG_ON in >control parser 2024-05-17 11:43:55 +02:00
LICENSES
mm x86/mm/pat: fix VM_PAT handling in COW mappings 2024-04-13 12:51:40 +02:00
net tcp: avoid premature drops in tcp_add_backlog() 2024-06-16 13:28:35 +02:00
samples
scripts
security
sound ASoC: da7219-aad: fix usage of device_get_named_child_node() 2024-06-16 13:28:31 +02:00
tools Revert "selftests: mm: fix map_hugetlb failure on 64K page size systems" 2024-05-25 16:17:17 +02:00
usr
virt KVM: async_pf: Cleanup kvm_setup_async_pf() 2024-05-02 16:18:32 +02:00
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Makefile Linux 5.4.277 2024-05-25 16:17:18 +02:00
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.

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.