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commit28df029d53upstream. A kernel exception was hit when trying to dump /proc/lockdep_chains after lockdep report "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!": Unable to handle kernel paging request at virtual address 00054005450e05c3 ... 00054005450e05c3] address between user and kernel address ranges ... pc : [0xffffffece769b3a8] string+0x50/0x10c lr : [0xffffffece769ac88] vsnprintf+0x468/0x69c ... Call trace: string+0x50/0x10c vsnprintf+0x468/0x69c seq_printf+0x8c/0xd8 print_name+0x64/0xf4 lc_show+0xb8/0x128 seq_read_iter+0x3cc/0x5fc proc_reg_read_iter+0xdc/0x1d4 The cause of the problem is the function lock_chain_get_class() will shift lock_classes index by 1, but the index don't need to be shifted anymore since commit01bb6f0af9("locking/lockdep: Change the range of class_idx in held_lock struct") already change the index to start from 0. The lock_classes[-1] located at chain_hlocks array. When printing lock_classes[-1] after the chain_hlocks entries are modified, the exception happened. The output of lockdep_chains are incorrect due to this problem too. Fixes:f611e8cf98("lockdep: Take read/write status in consideration when generate chainkey") Signed-off-by: Cheng Jui Wang <cheng-jui.wang@mediatek.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Link: https://lore.kernel.org/r/20220210105011.21712-1-cheng-jui.wang@mediatek.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.