c31b38cb94
llnode could be NULL if there are new allocations after the checking of c-free_cnt > c->high_watermark in bpf_mem_refill() and before the calling of __llist_del_first() in free_bulk (e.g. a PREEMPT_RT kernel or allocation in NMI context). And it will incur oops as shown below: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] PREEMPT_RT SMP CPU: 39 PID: 373 Comm: irq_work/39 Tainted: G W 6.0.0-rc6-rt9+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) RIP: 0010:bpf_mem_refill+0x66/0x130 ...... Call Trace: <TASK> irq_work_single+0x24/0x60 irq_work_run_list+0x24/0x30 run_irq_workd+0x18/0x20 smpboot_thread_fn+0x13f/0x2c0 kthread+0x121/0x140 ? kthread_complete_and_exit+0x20/0x20 ret_from_fork+0x1f/0x30 </TASK> Simply fixing it by checking whether or not llnode is NULL in free_bulk(). Fixes: 8d5a8011b35d ("bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.") Signed-off-by: Hou Tao <houtao1@huawei.com> Link: https://lore.kernel.org/r/20220919144811.3570825-1-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov <ast@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.