Message ID | 20091015161052.0752208e@marrow.netinsight.se |
---|---|
State | New, archived |
Headers | show |
* Simon Kagstrom <simon.kagstrom@netinsight.net> wrote: > The core functionality is implemented as per Linus suggestion from > > http://lists.infradead.org/pipermail/linux-mtd/2009-October/027620.html > > (with the kmsg_dump implementation by Linus). A struct kmsg_dumper has > been added which contains a callback to dump the kernel log buffers on > crashes. The kmsg_dump function gets called from oops_exit() and panic() > and invokes this callbacks with the crash reason. > > Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net> > Reviewed-by: Anders Grafstrom <anders.grafstrom@netinsight.net> The general structure looks very nice now! Assuming my review comments below are addressed all patches are: Reviewed-by: Ingo Molnar <mingo@elte.hu> > diff --git a/kernel/printk.c b/kernel/printk.c > index f38b07f..960406a 100644 > --- a/kernel/printk.c > +++ b/kernel/printk.c > @@ -33,6 +33,8 @@ > #include <linux/bootmem.h> > #include <linux/syscalls.h> > #include <linux/kexec.h> > +#include <linux/kmsg_dump.h> > +#include <linux/spinlock.h> ( Small nit: in theory the spinlock.h include should not be needed as printk.c already uses spinlocks and gets the types via mutex.h. ) > > #include <asm/uaccess.h> > > @@ -1405,3 +1407,105 @@ bool printk_timed_ratelimit(unsigned long *caller_jiffies, > } > EXPORT_SYMBOL(printk_timed_ratelimit); > #endif > + > +static LIST_HEAD(dump_list); > +static DEFINE_SPINLOCK(dump_list_lock); Please switch it around to be: static DEFINE_SPINLOCK(dump_list_lock); static LIST_HEAD(dump_list); as the lock will be cacheline aligned on SMP, so the list head can come after it 'for free'. If it's the other way around we'll use 8/16 more .data bytes on average. > + > +/** > + * kmsg_dump_register - register a kernel log dumper. > + * @dump: pointer to the kmsg_dumper structure > + * @priv: private data for the structure > + * > + * Adds a kernel log dumper to the system. The dump callback in the > + * structure will be called when the kernel oopses or panics and must be > + * set. Returns zero on success and -EINVAL or -EBUSY otherwise. > + */ > +int kmsg_dump_register(struct kmsg_dumper *dumper) > +{ > + unsigned long flags; > + > + /* The dump callback needs to be set */ > + if (!dumper->dump) > + return -EINVAL; > + > + /* Don't allow registering multiple times */ > + if (dumper->registered) > + return -EBUSY; > + > + dumper->registered = 1; > + > + spin_lock_irqsave(&dump_list_lock, flags); > + list_add(&dumper->list, &dump_list); > + spin_unlock_irqrestore(&dump_list_lock, flags); > + return 0; > +} > +EXPORT_SYMBOL(kmsg_dump_register); There's a race here: dumper->registered should be set to 1 inside the spinlock - to make the register/unregister API SMP safe. It probably doesnt matter much in practice right now (as the dumper will be registered during bootup and unregistered during shutdown), but still - it could matter to modular loading of multiple dumpers at once, in the future. Also, the check for ->registered should be done inside too. Plus a style nit: please put a newline before the 'return 0' - it looks more symmetric and separates the return from other code flow. > + > +/** > + * kmsg_dump_unregister - unregister a kmsg dumper. > + * @dump: pointer to the kmsg_dumper structure > + * > + * Removes a dump device from the system. > + */ > +void kmsg_dump_unregister(struct kmsg_dumper *dumper) > +{ > + unsigned long flags; > + > + spin_lock_irqsave(&dump_list_lock, flags); > + list_del(&dumper->list); > + spin_unlock_irqrestore(&dump_list_lock, flags); > +} > +EXPORT_SYMBOL(kmsg_dump_unregister); I'd suggest for this API to use an error return as well, and to do it safely - i.e. any combination of these APIs should result in a safe result. Right now a call sequence kmsg_dump_register() + kmsg_dump_unregister() + kmsg_dump_register() will corrupt memory. > + > +static const char *kmsg_reasons[] = { > + [KMSG_DUMP_OOPS] = "oops", > + [KMSG_DUMP_PANIC] = "panic", > +}; Should be 'const char const' for max constness. > +static const char *kmsg_to_str(enum kmsg_dump_reason reason) > +{ > + if (reason > ARRAY_SIZE(kmsg_reasons) || reason < 0) > + return "unknown"; That should be ">=" i guess, for the check to be correct. > + > + return kmsg_reasons[reason]; > +} > + > +/** > + * dump_kmsg - dump kernel log to kernel message dumpers. > + * @reason: the reason (oops, panic etc) for dumping > + * > + * Iterate through each of the dump devices and call the oops/panic > + * callbacks with the log buffer. > + */ > +void kmsg_dump(enum kmsg_dump_reason reason) > +{ > + unsigned long len = ACCESS_ONCE(log_end); > + struct kmsg_dumper *dumper; > + const char *s1, *s2; > + unsigned long l1, l2; > + > + s1 = ""; > + l1 = 0; > + s2 = log_buf; > + l2 = len; > + > + /* Have we rotated around the circular buffer? */ > + if (len > log_buf_len) { > + unsigned long pos = len & LOG_BUF_MASK; > + > + s1 = log_buf + pos; > + l1 = log_buf_len - pos; > + > + s2 = log_buf; > + l2 = pos; > + } > + > + if (!spin_trylock(&dump_list_lock)) { > + printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n", > + kmsg_to_str(reason)); > + return; > + } > + list_for_each_entry(dumper, &dump_list, list) > + dumper->dump(dumper, reason, s1, l1, s2, l2); > + spin_unlock(&dump_list_lock); > +} ( Might make sense to use _irqsave()/_irqrestore() variants here - so that if an IRQ comes in and panics too we dont recurse. The trylock protects us above, but we are already non-preempt here - going irqsafe is even better i guess. ) Ingo
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h new file mode 100644 index 0000000..4fb9d29 --- /dev/null +++ b/include/linux/kmsg_dump.h @@ -0,0 +1,36 @@ +/* + * linux/include/kmsg_dump.h + * + * Copyright (C) 2009 Net Insight AB + * + * Author: Simon Kagstrom <simon.kagstrom@netinsight.net> + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file COPYING in the main directory of this archive + * for more details. + */ +#ifndef _LINUX_KMSG_DUMP_H +#define _LINUX_KMSG_DUMP_H + +#include <linux/list.h> + +enum kmsg_dump_reason { + KMSG_DUMP_OOPS, + KMSG_DUMP_PANIC, +}; + +struct kmsg_dumper { + void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason, + const char *s1, unsigned long l1, + const char *s2, unsigned long l2); + struct list_head list; + int registered; +}; + +void kmsg_dump(enum kmsg_dump_reason reason); + +int kmsg_dump_register(struct kmsg_dumper *dumper); + +void kmsg_dump_unregister(struct kmsg_dumper *dumper); + +#endif /* _LINUX_DUMP_DEVICE_H */ diff --git a/kernel/panic.c b/kernel/panic.c index c0b33b8..763296d 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -10,6 +10,7 @@ */ #include <linux/debug_locks.h> #include <linux/interrupt.h> +#include <linux/kmsg_dump.h> #include <linux/kallsyms.h> #include <linux/notifier.h> #include <linux/module.h> @@ -76,6 +77,7 @@ NORET_TYPE void panic(const char * fmt, ...) dump_stack(); #endif + kmsg_dump(KMSG_DUMP_PANIC); /* * If we have crashed and we have a crash kernel loaded let it handle * everything else. @@ -341,6 +343,7 @@ void oops_exit(void) { do_oops_enter_exit(); print_oops_end_marker(); + kmsg_dump(KMSG_DUMP_OOPS); } #ifdef WANT_WARN_ON_SLOWPATH diff --git a/kernel/printk.c b/kernel/printk.c index f38b07f..960406a 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -33,6 +33,8 @@ #include <linux/bootmem.h> #include <linux/syscalls.h> #include <linux/kexec.h> +#include <linux/kmsg_dump.h> +#include <linux/spinlock.h> #include <asm/uaccess.h> @@ -1405,3 +1407,105 @@ bool printk_timed_ratelimit(unsigned long *caller_jiffies, } EXPORT_SYMBOL(printk_timed_ratelimit); #endif + +static LIST_HEAD(dump_list); +static DEFINE_SPINLOCK(dump_list_lock); + +/** + * kmsg_dump_register - register a kernel log dumper. + * @dump: pointer to the kmsg_dumper structure + * @priv: private data for the structure + * + * Adds a kernel log dumper to the system. The dump callback in the + * structure will be called when the kernel oopses or panics and must be + * set. Returns zero on success and -EINVAL or -EBUSY otherwise. + */ +int kmsg_dump_register(struct kmsg_dumper *dumper) +{ + unsigned long flags; + + /* The dump callback needs to be set */ + if (!dumper->dump) + return -EINVAL; + + /* Don't allow registering multiple times */ + if (dumper->registered) + return -EBUSY; + + dumper->registered = 1; + + spin_lock_irqsave(&dump_list_lock, flags); + list_add(&dumper->list, &dump_list); + spin_unlock_irqrestore(&dump_list_lock, flags); + return 0; +} +EXPORT_SYMBOL(kmsg_dump_register); + +/** + * kmsg_dump_unregister - unregister a kmsg dumper. + * @dump: pointer to the kmsg_dumper structure + * + * Removes a dump device from the system. + */ +void kmsg_dump_unregister(struct kmsg_dumper *dumper) +{ + unsigned long flags; + + spin_lock_irqsave(&dump_list_lock, flags); + list_del(&dumper->list); + spin_unlock_irqrestore(&dump_list_lock, flags); +} +EXPORT_SYMBOL(kmsg_dump_unregister); + +static const char *kmsg_reasons[] = { + [KMSG_DUMP_OOPS] = "oops", + [KMSG_DUMP_PANIC] = "panic", +}; + +static const char *kmsg_to_str(enum kmsg_dump_reason reason) +{ + if (reason > ARRAY_SIZE(kmsg_reasons) || reason < 0) + return "unknown"; + + return kmsg_reasons[reason]; +} + +/** + * dump_kmsg - dump kernel log to kernel message dumpers. + * @reason: the reason (oops, panic etc) for dumping + * + * Iterate through each of the dump devices and call the oops/panic + * callbacks with the log buffer. + */ +void kmsg_dump(enum kmsg_dump_reason reason) +{ + unsigned long len = ACCESS_ONCE(log_end); + struct kmsg_dumper *dumper; + const char *s1, *s2; + unsigned long l1, l2; + + s1 = ""; + l1 = 0; + s2 = log_buf; + l2 = len; + + /* Have we rotated around the circular buffer? */ + if (len > log_buf_len) { + unsigned long pos = len & LOG_BUF_MASK; + + s1 = log_buf + pos; + l1 = log_buf_len - pos; + + s2 = log_buf; + l2 = pos; + } + + if (!spin_trylock(&dump_list_lock)) { + printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n", + kmsg_to_str(reason)); + return; + } + list_for_each_entry(dumper, &dump_list, list) + dumper->dump(dumper, reason, s1, l1, s2, l2); + spin_unlock(&dump_list_lock); +}