Messages in this thread | | | From | John Ogness <> | Subject | [PATCH next v4 0/2] introduce printk cpu lock | Date | Thu, 17 Jun 2021 11:56:49 +0206 |
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Hello,
While working on removing the safe buffers for printk [0] we stumbled on a cpu-reentrant spinning lock used by dump_stack(). This type of lock (dubbed a cpu lock) will cause deadlock risks once we introduce atomic consoles because atomic consoles also need such a lock.
Although we are not yet ready to introduce atomic consoles, this is an appropriate time to provide an official cpu lock to be used for all things relating to printk (including the atomic consoles, once they are introduced).
An example of cpu lock usage for atomic consoles can be found in the PREEMPT_RT tree, such as the serial8250 implementation [1] of an atomic console. (In PREEMPT_RT the printk cpu lock function was named console_atomic_lock/_unlock.)
This series is against next-20210616.
v3 can be found here [2].
Changes since v3:
- Change @printk_cpulock_nested from a boolean to an atomic counter in order to track multiple levels of nesting.
- Correctly move over the original dump_stack() semantics by using atomic_set() to unlock.
- Move commit message note about disabling interrupts to the first patch.
John Ogness
[0] https://lore.kernel.org/lkml/YGW63%2FelFr%2FgYW1u@alley [1] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/drivers/tty/serial?h=v5.12-rc3-rt3&id=1aaca59df62710647243a3574fc27d93c2bd0e6c [2] https://lore.kernel.org/lkml/20210615174947.32057-1-john.ogness@linutronix.de
John Ogness (2): lib/dump_stack: move cpu lock to printk.c printk: fix cpu lock ordering
include/linux/printk.h | 41 +++++++++++++++ kernel/printk/printk.c | 116 +++++++++++++++++++++++++++++++++++++++++ lib/dump_stack.c | 38 +------------- 3 files changed, 159 insertions(+), 36 deletions(-)
-- 2.20.1
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