user/sven/linux.git/kernel/printk, branch v4.19.280

printk: fix return value of printk.devkmsg __setup handler

2022-04-15T12:14:45Z

[ Upstream commit b665eae7a788c5e2bc10f9ac3c0137aa0ad1fc97 ] If an invalid option value is used with "printk.devkmsg=", it is silently ignored. If a valid option value is used, it is honored but the wrong return value (0) is used, indicating that the command line option had an error and was not handled. This string is not added to init's environment strings due to init/main.c::unknown_bootoption() checking for a '.' in the boot option string and then considering that string to be an "Unused module parameter". Print a warning message if a bad option string is used. Always return 1 from the __setup handler to indicate that the command line option has been handled. Fixes: 750afe7babd1 ("printk: add kernel parameter to control writes to /dev/kmsg") Signed-off-by: Randy Dunlap Reported-by: Igor Zhbanov Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru Cc: Borislav Petkov Cc: Andrew Morton Cc: Petr Mladek Cc: Sergey Senozhatsky Cc: Steven Rostedt Cc: John Ogness Reviewed-by: John Ogness Reviewed-by: Sergey Senozhatsky Reviewed-by: Petr Mladek Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20220228220556.23484-1-rdunlap@infradead.org Signed-off-by: Sasha Levin

printk/console: Allow to disable console output by using console="" or console=null

2021-11-12T13:40:50Z

commit 3cffa06aeef7ece30f6b5ac0ea51f264e8fea4d0 upstream. The commit 48021f98130880dd74 ("printk: handle blank console arguments passed in.") prevented crash caused by empty console= parameter value. Unfortunately, this value is widely used on Chromebooks to disable the console output. The above commit caused performance regression because the messages were pushed on slow console even though nobody was watching it. Use ttynull driver explicitly for console="" and console=null parameters. It has been created for exactly this purpose. It causes that preferred_console is set. As a result, ttySX and ttyX are not used as a fallback. And only ttynull console gets registered by default. It still allows to register other consoles either by additional console= parameters or SPCR. It prevents regression because it worked this way even before. Also it is a sane semantic. Preventing output on all consoles should be done another way, for example, by introducing mute_console parameter. Link: https://lore.kernel.org/r/20201006025935.GA597@jagdpanzerIV.localdomain Suggested-by: Sergey Senozhatsky Reviewed-by: Guenter Roeck Tested-by: Guenter Roeck Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20201111135450.11214-3-pmladek@suse.com Cc: Yi Fan Signed-off-by: Greg Kroah-Hartman

printk: fix deadlock when kernel panic

2021-03-04T08:39:57Z

commit 8a8109f303e25a27f92c1d8edd67d7cbbc60a4eb upstream. printk_safe_flush_on_panic() caused the following deadlock on our server: CPU0: CPU1: panic rcu_dump_cpu_stacks kdump_nmi_shootdown_cpus nmi_trigger_cpumask_backtrace register_nmi_handler(crash_nmi_callback) printk_safe_flush __printk_safe_flush raw_spin_lock_irqsave(&read_lock) // send NMI to other processors apic_send_IPI_allbutself(NMI_VECTOR) // NMI interrupt, dead loop crash_nmi_callback printk_safe_flush_on_panic printk_safe_flush __printk_safe_flush // deadlock raw_spin_lock_irqsave(&read_lock) DEADLOCK: read_lock is taken on CPU1 and will never get released. It happens when panic() stops a CPU by NMI while it has been in the middle of printk_safe_flush(). Handle the lock the same way as logbuf_lock. The printk_safe buffers are flushed only when both locks can be safely taken. It can avoid the deadlock _in this particular case_ at expense of losing contents of printk_safe buffers. Note: It would actually be safe to re-init the locks when all CPUs were stopped by NMI. But it would require passing this information from arch-specific code. It is not worth the complexity. Especially because logbuf_lock and printk_safe buffers have been obsoleted by the lockless ring buffer. Fixes: cf9b1106c81c ("printk/nmi: flush NMI messages on the system panic") Signed-off-by: Muchun Song Reviewed-by: Petr Mladek Cc: Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210210034823.64867-1-songmuchun@bytedance.com Signed-off-by: Greg Kroah-Hartman

printk: handle blank console arguments passed in.

2020-10-01T11:14:45Z

[ Upstream commit 48021f98130880dd74286459a1ef48b5e9bc374f ] If uboot passes a blank string to console_setup then it results in a trashed memory. Ultimately, the kernel crashes during freeing up the memory. This fix checks if there is a blank parameter being passed to console_setup from uboot. In case it detects that the console parameter is blank then it doesn't setup the serial device and it gracefully exits. Link: https://lore.kernel.org/r/20200522065306.83-1-shreyas.joshi@biamp.com Signed-off-by: Shreyas Joshi Acked-by: Sergey Senozhatsky [pmladek@suse.com: Better format the commit message and code, remove unnecessary brackets.] Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: queue wake_up_klogd irq_work only if per-CPU areas are ready

2020-07-22T07:32:13Z

commit ab6f762f0f53162d41497708b33c9a3236d3609e upstream. printk_deferred(), similarly to printk_safe/printk_nmi, does not immediately attempt to print a new message on the consoles, avoiding calls into non-reentrant kernel paths, e.g. scheduler or timekeeping, which potentially can deadlock the system. Those printk() flavors, instead, rely on per-CPU flush irq_work to print messages from safer contexts. For same reasons (recursive scheduler or timekeeping calls) printk() uses per-CPU irq_work in order to wake up user space syslog/kmsg readers. However, only printk_safe/printk_nmi do make sure that per-CPU areas have been initialised and that it's safe to modify per-CPU irq_work. This means that, for instance, should printk_deferred() be invoked "too early", that is before per-CPU areas are initialised, printk_deferred() will perform illegal per-CPU access. Lech Perczak [0] reports that after commit 1b710b1b10ef ("char/random: silence a lockdep splat with printk()") user-space syslog/kmsg readers are not able to read new kernel messages. The reason is printk_deferred() being called too early (as was pointed out by Petr and John). Fix printk_deferred() and do not queue per-CPU irq_work before per-CPU areas are initialized. Link: https://lore.kernel.org/lkml/aa0732c6-5c4e-8a8b-a1c1-75ebe3dca05b@camlintechnologies.com/ Reported-by: Lech Perczak Signed-off-by: Sergey Senozhatsky Tested-by: Jann Horn Reviewed-by: Petr Mladek Cc: Greg Kroah-Hartman Cc: Theodore Ts'o Cc: John Ogness Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

printk: fix exclusive_console replaying

2020-02-11T12:33:51Z

[ Upstream commit def97da136515cb289a14729292c193e0a93bc64 ] Commit f92b070f2dc8 ("printk: Do not miss new messages when replaying the log") introduced a new variable @exclusive_console_stop_seq to store when an exclusive console should stop printing. It should be set to the @console_seq value at registration. However, @console_seq is previously set to @syslog_seq so that the exclusive console knows where to begin. This results in the exclusive console immediately reactivating all the other consoles and thus repeating the messages for those consoles. Set @console_seq after @exclusive_console_stop_seq has stored the current @console_seq value. Fixes: f92b070f2dc8 ("printk: Do not miss new messages when replaying the log") Link: http://lkml.kernel.org/r/20191219115322.31160-1-john.ogness@linutronix.de Cc: Steven Rostedt Cc: linux-kernel@vger.kernel.org Signed-off-by: John Ogness Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: fix integer overflow in setup_log_buf()

2019-12-01T08:16:14Z

[ Upstream commit d2130e82e9454304e9b91ba9da551b5989af8c27 ] The way we calculate logbuf free space percentage overflows signed integer: int free; free = __LOG_BUF_LEN - log_next_idx; pr_info("early log buf free: %u(%u%%)\n", free, (free * 100) / __LOG_BUF_LEN); We support LOG_BUF_LEN of up to 1<<25 bytes. Since setup_log_buf() is called during early init, logbuf is mostly empty, so __LOG_BUF_LEN - log_next_idx is close to 1<<25. Thus when we multiply it by 100, we overflow signed integer value range: 100 is 2^6 + 2^5 + 2^2. Example, booting with LOG_BUF_LEN 1<<25 and log_buf_len=2G boot param: [ 0.075317] log_buf_len: -2147483648 bytes [ 0.075319] early log buf free: 33549896(-28%) Make "free" unsigned integer and use appropriate printk() specifier. Link: http://lkml.kernel.org/r/20181010113308.9337-1-sergey.senozhatsky@gmail.com To: Steven Rostedt Cc: linux-kernel@vger.kernel.org Cc: Sergey Senozhatsky Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: lock/unlock console only for new logbuf entries

2019-12-01T08:16:13Z

[ Upstream commit 3ac37a93fa9217e576bebfd4ba3e80edaaeb2289 ] Prior to commit 5c2992ee7fd8a29 ("printk: remove console flushing special cases for partial buffered lines") we would do console_cont_flush() for each pr_cont() to print cont fragments, so console_unlock() would actually print data: pr_cont(); console_lock(); console_unlock() console_cont_flush(); // print cont fragment ... pr_cont(); console_lock(); console_unlock() console_cont_flush(); // print cont fragment We don't do console_cont_flush() anymore, so when we do pr_cont() console_unlock() does nothing (unless we flushed the cont buffer): pr_cont(); console_lock(); console_unlock(); // noop ... pr_cont(); console_lock(); console_unlock(); // noop ... pr_cont(); cont_flush(); console_lock(); console_unlock(); // print data We also wakeup klogd purposelessly for pr_cont() output - un-flushed cont buffer is not stored in log_buf; there is nothing to pull. Thus we can console_lock()/console_unlock()/wake_up_klogd() only when we know that we log_store()-ed a message and there is something to print to the consoles/syslog. Link: http://lkml.kernel.org/r/20181002023836.4487-3-sergey.senozhatsky@gmail.com To: Steven Rostedt Cc: Andrew Morton Cc: Dmitriy Vyukov Cc: Tetsuo Handa Cc: Tejun Heo Cc: Peter Zijlstra Cc: LKML Cc: Sergey Senozhatsky Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: Give error on attempt to set log buffer length to over 2G

2019-11-24T07:20:46Z

[ Upstream commit e6fe3e5b7d16e8f146a4ae7fe481bc6e97acde1e ] The current printk() is ready to handle log buffer size up to 2G. Give an explicit error for users who want to use larger log buffer. Also fix printk formatting to show the 2G as a positive number. Link: http://lkml.kernel.org/r/20181008135916.gg4kkmoki5bgtco5@pathway.suse.cz Cc: rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org Suggested-by: Sergey Senozhatsky Signed-off-by: He Zhe Reviewed-by: Sergey Senozhatsky [pmladek: Fixed to the really safe limit 2GB.] Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin

printk: Correct wrong casting

2019-11-24T07:20:24Z

[ Upstream commit 51a72ab7372d85c96104e58036f1b49ba11e5d2b ] log_first_seq and console_seq are 64-bit unsigned integers. Correct a wrong casting that might cut off the output. Link: http://lkml.kernel.org/r/1538239553-81805-2-git-send-email-zhe.he@windriver.com Cc: rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org Signed-off-by: He Zhe [sergey.senozhatsky@gmail.com: More descriptive commit message] Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin