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Mark noticed that syzkaller is able to reliably trigger the following warning: dl_rq->running_bw > dl_rq->this_bw WARNING: CPU: 1 PID: 153 at kernel/sched/deadline.c:124 switched_from_dl+0x454/0x608 Kernel panic - not syncing: panic_on_warn set ... CPU: 1 PID: 153 Comm: syz-executor253 Not tainted 4.18.0-rc3+ #29 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x458 show_stack+0x20/0x30 dump_stack+0x180/0x250 panic+0x2dc/0x4ec __warn_printk+0x0/0x150 report_bug+0x228/0x2d8 bug_handler+0xa0/0x1a0 brk_handler+0x2f0/0x568 do_debug_exception+0x1bc/0x5d0 el1_dbg+0x18/0x78 switched_from_dl+0x454/0x608 __sched_setscheduler+0x8cc/0x2018 sys_sched_setattr+0x340/0x758 el0_svc_naked+0x30/0x34 syzkaller reproducer runs a bunch of threads that constantly switch between DEADLINE and NORMAL classes while interacting through futexes. The splat above is caused by the fact that if a DEADLINE task is setattr back to NORMAL while in non_contending state (blocked on a futex - inactive timer armed), its contribution to running_bw is not removed before sub_rq_bw() gets called (!task_on_rq_queued() branch) and the latter sees running_bw > this_bw. Fix it by removing a task contribution from running_bw if the task is not queued and in non_contending state while switched to a different class. Reported-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com> Reviewed-by: Luca Abeni <luca.abeni@santannapisa.it> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: claudio@evidence.eu.com Cc: rostedt@goodmis.org Link: http://lkml.kernel.org/r/20180711072948.27061-1-juri.lelli@redhat.com Signed-off-by: Ingo Molnar <mingo@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.
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.