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Rafael J. Wysocki
a72173ecfc
Revert commitc22397888f"exec: make de_thread() freezable" as requested by Ingo Molnar: "So there's a new regression in v4.20-rc4, my desktop produces this lockdep splat: [ 1772.588771] WARNING: pkexec/4633 still has locks held! [ 1772.588773] 4.20.0-rc4-custom-00213-g93a49841322b #1 Not tainted [ 1772.588775] ------------------------------------ [ 1772.588776] 1 lock held by pkexec/4633: [ 1772.588778] #0: 00000000ed85fbf8 (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds+0x2a/0x70 [ 1772.588786] stack backtrace: [ 1772.588789] CPU: 7 PID: 4633 Comm: pkexec Not tainted 4.20.0-rc4-custom-00213-g93a49841322b #1 [ 1772.588792] Call Trace: [ 1772.588800] dump_stack+0x85/0xcb [ 1772.588803] flush_old_exec+0x116/0x890 [ 1772.588807] ? load_elf_phdrs+0x72/0xb0 [ 1772.588809] load_elf_binary+0x291/0x1620 [ 1772.588815] ? sched_clock+0x5/0x10 [ 1772.588817] ? search_binary_handler+0x6d/0x240 [ 1772.588820] search_binary_handler+0x80/0x240 [ 1772.588823] load_script+0x201/0x220 [ 1772.588825] search_binary_handler+0x80/0x240 [ 1772.588828] __do_execve_file.isra.32+0x7d2/0xa60 [ 1772.588832] ? strncpy_from_user+0x40/0x180 [ 1772.588835] __x64_sys_execve+0x34/0x40 [ 1772.588838] do_syscall_64+0x60/0x1c0 The warning gets triggered by an ancient lockdep check in the freezer: (gdb) list *0xffffffff812ece06 0xffffffff812ece06 is in flush_old_exec (./include/linux/freezer.h:57). 52 * DO NOT ADD ANY NEW CALLERS OF THIS FUNCTION 53 * If try_to_freeze causes a lockdep warning it means the caller may deadlock 54 */ 55 static inline bool try_to_freeze_unsafe(void) 56 { 57 might_sleep(); 58 if (likely(!freezing(current))) 59 return false; 60 return __refrigerator(false); 61 } I reviewed the ->cred_guard_mutex code, and the mutex is held across all of exec() - and we always did this. But there's this recent -rc4 commit: > Chanho Min (1): > exec: make de_thread() freezablec22397888f: exec: make de_thread() freezable I believe this commit is bogus, you cannot call try_to_freeze() from de_thread(), because it's holding the ->cred_guard_mutex." Reported-by: Ingo Molnar <mingo@kernel.org> Tested-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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.