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If you build a kernel with CONFIG_PREEMPTION=n and CONFIG_PREEMPT_COUNT=y, then run the rcutorture tests specifying stalls as follows: runqemu kvm slirp nographic qemuparams="-m 1024 -smp 4" \ bootparams="console=ttyS0 rcutorture.stall_cpu=30 \ rcutorture.stall_no_softlockup=1 rcutorture.stall_cpu_block=1" -d The tests will produce the following splat: [ 10.841071] rcu-torture: rcu_torture_stall begin CPU stall [ 10.841073] rcu_torture_stall start on CPU 3. [ 10.841077] BUG: scheduling while atomic: rcu_torture_sta/66/0x0000000 .... [ 10.841108] Call Trace: [ 10.841110] <TASK> [ 10.841112] dump_stack_lvl+0x64/0xb0 [ 10.841118] dump_stack+0x10/0x20 [ 10.841121] __schedule_bug+0x8b/0xb0 [ 10.841126] __schedule+0x2172/0x2940 [ 10.841157] schedule+0x9b/0x150 [ 10.841160] schedule_timeout+0x2e8/0x4f0 [ 10.841192] schedule_timeout_uninterruptible+0x47/0x50 [ 10.841195] rcu_torture_stall+0x2e8/0x300 [ 10.841199] kthread+0x175/0x1a0 [ 10.841206] ret_from_fork+0x2c/0x50 This is because the rcutorture.stall_cpu_block=1 module parameter causes rcu_torture_stall() to invoke schedule_timeout_uninterruptible() within an RCU read-side critical section. This in turn results in a quiescent state (which prevents the stall) and a sleep in an atomic context (which produces the above splat). Although this code is operating as designed, the design has proven to be counterintuitive to many. This commit therefore updates the description in kernel-parameters.txt accordingly. [ paulmck: Apply Joel Fernandes feedback. ] Signed-off-by: Zqiang <qiang1.zhang@intel.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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.