a35a76faad
Yonghong Song says: ==================== Commit8b401f9ed2("bpf: implement bpf_send_signal() helper") introduced bpf_send_signal() helper and Commit8482941f09("bpf: Add bpf_send_signal_thread() helper") added bpf_send_signal_thread() helper. Both helpers try to send a signel to current process or thread. When bpf_prog is called with scheduler rq_lock held, a deadlock could happen since bpf_send_signal() and bpf_send_signal_thread() will call group_send_sig_info() which may ultimately want to acquire rq_lock() again. This happens in 5.2 and 4.16 based kernels in our production environment with perf_sw_event. In a different scenario, the following is also possible in the last kernel: cpu 1: do_task_stat <- holding sighand->siglock ... task_sched_runtime <- trying to grab rq_lock cpu 2: __schedule <- holding rq_lock ... do_send_sig_info <- trying to grab sighand->siglock Commiteac9153f2b("bpf/stackmap: Fix deadlock with rq_lock in bpf_get_stack()") has a similar issue with above rq_lock() deadlock. This patch set addressed the issue in a similar way. Patch #1 provided kernel solution and Patch #2 added a selftest. Changelogs: v2 -> v3: . simplify selftest send_signal_sched_switch(). The previous version has mmap/munmap inherited from Song's reproducer. They are not necessary in this context. v1 -> v2: . previous fix using task_work in nmi() is incorrect. there is no nmi() involvement here. Using task_work in all cases might be a solution. But decided to use a similar fix as in Commiteac9153f2b. ==================== 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.