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authorSergey Senozhatsky <sergey.senozhatsky@gmail.com>2020-03-03 20:30:02 +0900
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-10 13:18:57 -0700
commitab6f762f0f53162d41497708b33c9a3236d3609e (patch)
treee0d405ac3f1a4c99cc46609cb24bc64ee5cfea19 /include
parent87ad46e601340394cd75c1c79b19ca906f82c543 (diff)
downloadlinux-ab6f762f0f53162d41497708b33c9a3236d3609e.tar.bz2
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 'include')
-rw-r--r--include/linux/printk.h5
1 files changed, 0 insertions, 5 deletions
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 1e6108b8d15f..e061635e0409 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -202,7 +202,6 @@ __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...);
void dump_stack_print_info(const char *log_lvl);
void show_regs_print_info(const char *log_lvl);
extern asmlinkage void dump_stack(void) __cold;
-extern void printk_safe_init(void);
extern void printk_safe_flush(void);
extern void printk_safe_flush_on_panic(void);
#else
@@ -269,10 +268,6 @@ static inline void dump_stack(void)
{
}
-static inline void printk_safe_init(void)
-{
-}
-
static inline void printk_safe_flush(void)
{
}