94b7cc01da
Syzbot reported the below lockdep splat:
WARNING: possible irq lock inversion dependency detected
5.6.0-rc7-syzkaller #0 Not tainted
--------------------------------------------------------
syz-executor.0/10317 just changed the state of lock:
ffff888021d16568 (&(&info->lock)->rlock){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline]
ffff888021d16568 (&(&info->lock)->rlock){+.+.}, at: shmem_mfill_atomic_pte+0x1012/0x21c0 mm/shmem.c:2407
but this lock was taken by another, SOFTIRQ-safe lock in the past:
(&(&xa->xa_lock)->rlock#5){..-.}
and interrupts could create inverse lock ordering between them.
other info that might help us debug this:
Possible interrupt unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&(&info->lock)->rlock);
local_irq_disable();
lock(&(&xa->xa_lock)->rlock#5);
lock(&(&info->lock)->rlock);
<Interrupt>
lock(&(&xa->xa_lock)->rlock#5);
*** DEADLOCK ***
The full report is quite lengthy, please see:
https://lore.kernel.org/linux-mm/alpine.LSU.2.11.2004152007370.13597@eggly.anvils/T/#m813b412c5f78e25ca8c6c7734886ed4de43f241d
It is because CPU 0 held info->lock with IRQ enabled in userfaultfd_copy
path, then CPU 1 is splitting a THP which held xa_lock and info->lock in
IRQ disabled context at the same time. If softirq comes in to acquire
xa_lock, the deadlock would be triggered.
The fix is to acquire/release info->lock with *_irq version instead of
plain spin_{lock,unlock} to make it softirq safe.
Fixes:
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|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.