38b407be17
Currently the spu coredump code triggers an RCU warning: ============================= WARNING: suspicious RCU usage 5.7.0-rc3-01755-g7cd49f0b7ec7 #1 Not tainted ----------------------------- include/linux/fdtable.h:95 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 1 lock held by spu-coredump/1343: #0: c0000007fa22f430 (sb_writers#2){.+.+}-{0:0}, at: .do_coredump+0x1010/0x13c8 stack backtrace: CPU: 0 PID: 1343 Comm: spu-coredump Not tainted 5.7.0-rc3-01755-g7cd49f0b7ec7 #1 Call Trace: .dump_stack+0xec/0x15c (unreliable) .lockdep_rcu_suspicious+0x120/0x144 .coredump_next_context+0x148/0x158 .spufs_coredump_extra_notes_size+0x54/0x190 .elf_coredump_extra_notes_size+0x34/0x50 .elf_core_dump+0xe48/0x19d0 .do_coredump+0xe50/0x13c8 .get_signal+0x864/0xd88 .do_notify_resume+0x158/0x3c8 .interrupt_exit_user_prepare+0x19c/0x208 interrupt_return+0x14/0x1c0 This comes from fcheck_files() via fcheck(). It's pretty clearly documented that fcheck() must be wrapped with rcu_read_lock(), adding that fixes the RCU warning. hch points out that once we've released the RCU read lock the file may be closed and freed, which would leave us with a pointer to a freed spu_context. To avoid that, take a reference to the spu_context while we hold the RCU read lock, and drop that reference later once we're done with the context. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200508130633.2532759-1-mpe@ellerman.id.au
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.