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| author | Sergey Senozhatsky <sergey.senozhatsky@gmail.com> | 2020-03-03 20:30:02 +0900 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-04-10 13:18:57 -0700 |
| commit | ab6f762f0f53162d41497708b33c9a3236d3609e (patch) | |
| tree | e0d405ac3f1a4c99cc46609cb24bc64ee5cfea19 /kernel/printk/internal.h | |
| parent | 87ad46e601340394cd75c1c79b19ca906f82c543 (diff) | |
| download | linux-ab6f762f0f53162d41497708b33c9a3236d3609e.tar.gz linux-ab6f762f0f53162d41497708b33c9a3236d3609e.tar.bz2 linux-ab6f762f0f53162d41497708b33c9a3236d3609e.zip | |
printk: queue wake_up_klogd irq_work only if per-CPU areas are ready
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 <l.perczak@camlintechnologies.com>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Tested-by: Jann Horn <jannh@google.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/printk/internal.h')
| -rw-r--r-- | kernel/printk/internal.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index c8e6ab689d42..b2b0f526f249 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -23,6 +23,9 @@ __printf(1, 0) int vprintk_func(const char *fmt, va_list args); void __printk_safe_enter(void); void __printk_safe_exit(void); +void printk_safe_init(void); +bool printk_percpu_data_ready(void); + #define printk_safe_enter_irqsave(flags) \ do { \ local_irq_save(flags); \ @@ -64,4 +67,6 @@ __printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; } #define printk_safe_enter_irq() local_irq_disable() #define printk_safe_exit_irq() local_irq_enable() +static inline void printk_safe_init(void) { } +static inline bool printk_percpu_data_ready(void) { return false; } #endif /* CONFIG_PRINTK */ |