linux/kernel/printk, branch v5.14

Merge tag 'printk-for-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

2021-06-29T19:07:18Z

Pull printk updates from Petr Mladek: - Add %pt[RT]s modifier to vsprintf(). It overrides ISO 8601 separator by using ' ' (space). It produces "YYYY-mm-dd HH:MM:SS" instead of "YYYY-mm-ddTHH:MM:SS". - Correctly parse long row of numbers by sscanf() when using the field width. Add extensive sscanf() selftest. - Generalize re-entrant CPU lock that has already been used to serialize dump_stack() output. It is part of the ongoing printk rework. It will allow to remove the obsoleted printk_safe buffers and introduce atomic consoles. - Some code clean up and sparse warning fixes. * tag 'printk-for-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: printk: fix cpu lock ordering lib/dump_stack: move cpu lock to printk.c printk: Remove trailing semicolon in macros random32: Fix implicit truncation warning in prandom_seed_state() lib: test_scanf: Remove pointless use of type_min() with unsigned types selftests: lib: Add wrapper script for test_scanf lib: test_scanf: Add tests for sscanf number conversion lib: vsprintf: Fix handling of number field widths in vsscanf lib: vsprintf: scanf: Negative number must have field width > 1 usb: host: xhci-tegra: Switch to use %ptTs nilfs2: Switch to use %ptTs kdb: Switch to use %ptTs lib/vsprintf: Allow to override ISO 8601 date and time separator

printk: fix cpu lock ordering

2021-06-22T07:57:15Z

The cpu lock implementation uses a full memory barrier to take the lock, but no memory barriers when releasing the lock. This means that changes performed by a lock owner may not be seen by the next lock owner. This may have been "good enough" for use by dump_stack() as a serialization mechanism, but it is not enough to provide proper protection for a critical section. Correct this problem by using acquire/release memory barriers for lock/unlock, respectively. Signed-off-by: John Ogness Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210617095051.4808-3-john.ogness@linutronix.de

lib/dump_stack: move cpu lock to printk.c

2021-06-22T07:56:10Z

dump_stack() implements its own cpu-reentrant spinning lock to best-effort serialize stack traces in the printk log. However, there are other functions (such as show_regs()) that can also benefit from this serialization. Move the cpu-reentrant spinning lock (cpu lock) into new helper functions printk_cpu_lock_irqsave()/printk_cpu_unlock_irqrestore() so that it is available for others as well. For !CONFIG_SMP the cpu lock is a NOP. Note that having multiple cpu locks in the system can easily lead to deadlock. Code needing a cpu lock should use the printk cpu lock, since the printk cpu lock could be acquired from any code and any context. Also note that it is not necessary for a cpu lock to disable interrupts. However, in upcoming work this cpu lock will be used for emergency tasks (for example, atomic consoles during kernel crashes) and any interruptions while holding the cpu lock should be avoided if possible. Signed-off-by: John Ogness Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek [pmladek@suse.com: Backported on top of 5.13-rc1.] Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210617095051.4808-2-john.ogness@linutronix.de

printk: Move EXPORT_SYMBOL() closer to vprintk definition

2021-06-16T08:42:19Z

Commit 28e1745b9fa2 ("printk: rename vprintk_func to vprintk") while improving readability by removing vprintk indirection, inadvertently placed the EXPORT_SYMBOL() for the newly renamed function at the end of the file. For reader sanity, and as is convention move the EXPORT_SYMBOL() declaration just after the end of the function. Fixes: 28e1745b9fa2 ("printk: rename vprintk_func to vprintk") Signed-off-by: Punit Agrawal Acked-by: Rasmus Villemoes Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210614235635.887365-1-punitagrawal@gmail.com

kernel/printk.c: Fixed mundane typos

2021-03-30T13:34:17Z

s/sempahore/semaphore/ s/exacly/exactly/ s/unregistred/unregistered/ s/interation/iteration/ Signed-off-by: Bhaskar Chowdhury Reviewed-by: Petr Mladek [pmladek@suse.com: Removed 4th hunk. The string has already been removed in the meantime.] Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210328043932.8310-1-unixbhaskar@gmail.com

printk: rename vprintk_func to vprintk

2021-03-30T13:21:18Z

The printk code is already hard enough to understand. Remove an unnecessary indirection by renaming vprintk_func to vprintk (adding the asmlinkage annotation), and removing the vprintk definition from printk.c. That way, printk is implemented in terms of vprintk as one would expect, and there's no "vprintk_func, what's that? Some function pointer that gets set where?" The declaration of vprintk in linux/printk.h already has the __printf(1,0) attribute, there's no point repeating that with the definition - it's for diagnostics in callers. linux/printk.h already contains a static inline {return 0;} definition of vprintk when !CONFIG_PRINTK. Since the corresponding stub definition of vprintk_func was not marked "static inline", any translation unit including internal.h would get a definition of vprintk_func - it just so happens that for !CONFIG_PRINTK, there is precisely one such TU, namely printk.c. Had there been more, it would be a link error; now it's just a silly waste of a few bytes of .text, which one must assume are rather precious to anyone disabling PRINTK. $ objdump -dr kernel/printk/printk.o 00000330 : 330: 31 c0 xor %eax,%eax 332: c3 ret 333: 8d b4 26 00 00 00 00 lea 0x0(%esi,%eiz,1),%esi 33a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi Signed-off-by: Rasmus Villemoes Reviewed-by: Steven Rostedt (VMware) Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210323144201.486050-1-linux@rasmusvillemoes.dk

printk: console: remove unnecessary safe buffer usage

2021-03-08T10:43:38Z

Upon registering a console, safe buffers are activated when setting up the sequence number to replay the log. However, these are already protected by @console_sem and @syslog_lock. Remove the unnecessary safe buffer usage. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210303101528.29901-16-john.ogness@linutronix.de

printk: kmsg_dump: remove _nolock() variants

2021-03-08T10:43:35Z

kmsg_dump_rewind() and kmsg_dump_get_line() are lockless, so there is no need for _nolock() variants. Remove these functions and switch all callers of the _nolock() variants. The functions without _nolock() were chosen because they are already exported to kernel modules. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210303101528.29901-15-john.ogness@linutronix.de

printk: remove logbuf_lock

2021-03-08T10:43:32Z

Since the ringbuffer is lockless, there is no need for it to be protected by @logbuf_lock. Remove @logbuf_lock. @console_seq, @exclusive_console_stop_seq, @console_dropped are protected by @console_lock. Signed-off-by: John Ogness Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210303101528.29901-14-john.ogness@linutronix.de

printk: introduce a kmsg_dump iterator

2021-03-08T10:43:27Z

Rather than storing the iterator information in the registered kmsg_dumper structure, create a separate iterator structure. The kmsg_dump_iter structure can reside on the stack of the caller, thus allowing lockless use of the kmsg_dump functions. Update code that accesses the kernel logs using the kmsg_dumper structure to use the new kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a call to kmsg_dump_rewind() to initialize the iterator. All this is in preparation for removal of @logbuf_lock. Signed-off-by: John Ogness Reviewed-by: Kees Cook # pstore Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210303101528.29901-13-john.ogness@linutronix.de