735e7a12a6
[ Upstream commit ce5c31db3645b649a31044a4d8b6057f6c723702 ] At the moment, UBSAN report will be serialized using a spin_lock(). On RT-systems, spinlocks are turned to rt_spin_lock and may sleep. This will result to the following splat if the undefined behavior is in a context that can sleep: BUG: sleeping function called from invalid context at /src/linux/kernel/locking/rtmutex.c:968 in_atomic(): 1, irqs_disabled(): 128, pid: 3447, name: make 1 lock held by make/3447: #0: 000000009a966332 (&mm->mmap_sem){++++}, at: do_page_fault+0x140/0x4f8 irq event stamp: 6284 hardirqs last enabled at (6283): [<ffff000011326520>] _raw_spin_unlock_irqrestore+0x90/0xa0 hardirqs last disabled at (6284): [<ffff0000113262b0>] _raw_spin_lock_irqsave+0x30/0x78 softirqs last enabled at (2430): [<ffff000010088ef8>] fpsimd_restore_current_state+0x60/0xe8 softirqs last disabled at (2427): [<ffff000010088ec0>] fpsimd_restore_current_state+0x28/0xe8 Preemption disabled at: [<ffff000011324a4c>] rt_mutex_futex_unlock+0x4c/0xb0 CPU: 3 PID: 3447 Comm: make Tainted: G W 5.2.14-rt7-01890-ge6e057589653 #911 Call trace: dump_backtrace+0x0/0x148 show_stack+0x14/0x20 dump_stack+0xbc/0x104 ___might_sleep+0x154/0x210 rt_spin_lock+0x68/0xa0 ubsan_prologue+0x30/0x68 handle_overflow+0x64/0xe0 __ubsan_handle_add_overflow+0x10/0x18 __lock_acquire+0x1c28/0x2a28 lock_acquire+0xf0/0x370 _raw_spin_lock_irqsave+0x58/0x78 rt_mutex_futex_unlock+0x4c/0xb0 rt_spin_unlock+0x28/0x70 get_page_from_freelist+0x428/0x2b60 __alloc_pages_nodemask+0x174/0x1708 alloc_pages_vma+0x1ac/0x238 __handle_mm_fault+0x4ac/0x10b0 handle_mm_fault+0x1d8/0x3b0 do_page_fault+0x1c8/0x4f8 do_translation_fault+0xb8/0xe0 do_mem_abort+0x3c/0x98 el0_da+0x20/0x24 The spin_lock() will protect against multiple CPUs to output a report together, I guess to prevent them from being interleaved. However, they can still interleave with other messages (and even splat from __might_sleep). So the lock usefulness seems pretty limited. Rather than trying to accomodate RT-system by switching to a raw_spin_lock(), the lock is now completely dropped. Link: http://lkml.kernel.org/r/20190920100835.14999-1-julien.grall@arm.com Signed-off-by: Julien Grall <julien.grall@arm.com> Reported-by: Andre Przywara <andre.przywara@arm.com> Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@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.