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SubjectRe: [PATCH 08/28] kdb: core for kgdb back end (2 of 2)
Jason Wessel <jason.wessel@windriver.com> writes:

> This patch contains the hooks and instrumentation into kernel which
> live outside the kernel/debug directory, which the kdb core
> will call to run commands like lsmod, dmesg, bt etc...

You know this dropping the locks from vmalloc_info and swap_info
is down right ugly, and I don't believe it is safe. That code
was not designed to run while the write_lock is held.

How does kdb build if NOMMU is set?

Similarly with si_swapinfo. What makes it safe to run the
code without it's locks. Safe as in no null pointer deferences
or other nasties.

I am not impressed with the mess you make of meminfo_proc_show.
That looks like a maintenance hazard if I ever saw one. An innocent
change to get some additional info (that happens to take a lock)
will cause kdb to deadlock.

The weird magic include of kdb.h in fs/proc/meminfo.c is also ugly.

Eric

> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index 1f24a3e..36d55e1 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -32,11 +32,11 @@ extern struct mm_struct *mm_for_maps(struct task_struct *);
>
> #ifdef CONFIG_MMU
> #define VMALLOC_TOTAL (VMALLOC_END - VMALLOC_START)
> -extern void get_vmalloc_info(struct vmalloc_info *vmi);
> +extern void get_vmalloc_info(struct vmalloc_info *vmi, int lock);
> #else
>
> #define VMALLOC_TOTAL 0UL
> -#define get_vmalloc_info(vmi) \
> +#define get_vmalloc_info(vmi, lock) \
> do { \
> (vmi)->used = 0; \
> (vmi)->largest_chunk = 0; \
> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index a65239c..b967cf2 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -10,6 +10,7 @@
> #include <linux/seq_file.h>
> #include <linux/swap.h>
> #include <linux/vmstat.h>
> +#include <linux/kdb.h>
> #include <asm/atomic.h>
> #include <asm/page.h>
> #include <asm/pgtable.h>
> @@ -19,7 +20,7 @@ void __attribute__((weak)) arch_report_meminfo(struct seq_file *m)
> {
> }
>
> -static int meminfo_proc_show(struct seq_file *m, void *v)
> +int _meminfo_proc_show(struct seq_file *m, void *v, int lock)
> {
> struct sysinfo i;
> unsigned long committed;
> @@ -34,7 +35,10 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
> */
> #define K(x) ((x) << (PAGE_SHIFT - 10))
> si_meminfo(&i);
> - si_swapinfo(&i);
> + if (lock)
> + si_swapinfo(&i);
> + else
> + __si_swapinfo(&i);
> committed = percpu_counter_read_positive(&vm_committed_as);
> allowed = ((totalram_pages - hugetlb_total_pages())
> * sysctl_overcommit_ratio / 100) + total_swap_pages;
> @@ -44,7 +48,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
> if (cached < 0)
> cached = 0;
>
> - get_vmalloc_info(&vmi);
> + get_vmalloc_info(&vmi, lock);
>
> for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
> pages[lru] = global_page_state(NR_LRU_BASE + lru);
> @@ -161,6 +165,11 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
> #undef K
> }
>
> +static int meminfo_proc_show(struct seq_file *m, void *v)
> +{
> + return _meminfo_proc_show(m, v, 1);
> +}
> +
> static int meminfo_proc_open(struct inode *inode, struct file *file)
> {
> return single_open(file, meminfo_proc_show, NULL);
> diff --git a/fs/proc/mmu.c b/fs/proc/mmu.c
> index 8ae221d..10a0f8b 100644
> --- a/fs/proc/mmu.c
> +++ b/fs/proc/mmu.c
> @@ -14,7 +14,7 @@
> #include <asm/pgtable.h>
> #include "internal.h"
>
> -void get_vmalloc_info(struct vmalloc_info *vmi)
> +void get_vmalloc_info(struct vmalloc_info *vmi, int lock)
> {
> struct vm_struct *vma;
> unsigned long free_area_size;
> @@ -30,7 +30,8 @@ void get_vmalloc_info(struct vmalloc_info *vmi)
>
> prev_end = VMALLOC_START;
>
> - read_lock(&vmlist_lock);
> + if (lock)
> + read_lock(&vmlist_lock);
>
> for (vma = vmlist; vma; vma = vma->next) {
> unsigned long addr = (unsigned long) vma->addr;
> @@ -55,6 +56,7 @@ void get_vmalloc_info(struct vmalloc_info *vmi)
> if (VMALLOC_END - prev_end > vmi->largest_chunk)
> vmi->largest_chunk = VMALLOC_END - prev_end;
>
> - read_unlock(&vmlist_lock);
> + if (lock)
> + read_unlock(&vmlist_lock);
> }
> }
> diff --git a/include/asm-generic/kmap_types.h b/include/asm-generic/kmap_types.h
> index e5f234a..97e807c 100644
> --- a/include/asm-generic/kmap_types.h
> +++ b/include/asm-generic/kmap_types.h
> @@ -28,7 +28,8 @@ KMAP_D(15) KM_UML_USERCOPY,
> KMAP_D(16) KM_IRQ_PTE,
> KMAP_D(17) KM_NMI,
> KMAP_D(18) KM_NMI_PTE,
> -KMAP_D(19) KM_TYPE_NR
> +KMAP_D(19) KM_KDB,
> +KMAP_D(20) KM_TYPE_NR
> };
>
> #undef KMAP_D
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index a2602a8..c326282 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -312,6 +312,7 @@ extern struct page *swapin_readahead(swp_entry_t, gfp_t,
> /* linux/mm/swapfile.c */
> extern long nr_swap_pages;
> extern long total_swap_pages;
> +extern void __si_swapinfo(struct sysinfo *);
> extern void si_swapinfo(struct sysinfo *);
> extern swp_entry_t get_swap_page(void);
> extern swp_entry_t get_swap_page_of_type(int);
> @@ -377,6 +378,7 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
>
> #define si_swapinfo(val) \
> do { (val)->freeswap = (val)->totalswap = 0; } while (0)
> +#define __si_swapinfo(val) si_swapinfo(val)
> /* only sparc can not include linux/pagemap.h in this file
> * so leave page_cache_release and release_pages undeclared... */
> #define free_page_and_swap_cache(page) \
> diff --git a/init/main.c b/init/main.c
> index 4cb47a1..9d415a1 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -63,6 +63,7 @@
> #include <linux/sched.h>
> #include <linux/signal.h>
> #include <linux/idr.h>
> +#include <linux/kdb.h>
> #include <linux/ftrace.h>
> #include <linux/async.h>
> #include <linux/kmemcheck.h>
> @@ -659,6 +660,7 @@ asmlinkage void __init start_kernel(void)
> key_init();
> radix_tree_init();
> security_init();
> + kdb_init(KDB_INIT_FULL);
> vfs_caches_init(totalram_pages);
> signals_init();
> /* rootfs populating might need page-writeback */
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 8e5288a..dc08f8b 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -16,6 +16,7 @@
> #include <linux/init.h>
> #include <linux/seq_file.h>
> #include <linux/fs.h>
> +#include <linux/kdb.h>
> #include <linux/err.h>
> #include <linux/proc_fs.h>
> #include <linux/sched.h> /* for cond_resched */
> @@ -515,6 +516,26 @@ static int kallsyms_open(struct inode *inode, struct file *file)
> return ret;
> }
>
> +#ifdef CONFIG_KGDB_KDB
> +const char *kdb_walk_kallsyms(loff_t *pos)
> +{
> + static struct kallsym_iter kdb_walk_kallsyms_iter;
> + if (*pos == 0) {
> + memset(&kdb_walk_kallsyms_iter, 0,
> + sizeof(kdb_walk_kallsyms_iter));
> + reset_iter(&kdb_walk_kallsyms_iter, 0);
> + }
> + while (1) {
> + if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
> + return NULL;
> + ++*pos;
> + /* Some debugging symbols have no name. Ignore them. */
> + if (kdb_walk_kallsyms_iter.name[0])
> + return kdb_walk_kallsyms_iter.name;
> + }
> +}
> +#endif /* CONFIG_KGDB_KDB */
> +
> static const struct file_operations kallsyms_operations = {
> .open = kallsyms_open,
> .read = seq_read,
> diff --git a/kernel/module.c b/kernel/module.c
> index f82386b..e59aca1 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -79,6 +79,10 @@ EXPORT_TRACEPOINT_SYMBOL(module_get);
> DEFINE_MUTEX(module_mutex);
> EXPORT_SYMBOL_GPL(module_mutex);
> static LIST_HEAD(modules);
> +#ifdef CONFIG_KGDB_KDB
> +struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
> +#endif /* CONFIG_KGDB_KDB */
> +
>
> /* Block module loading/unloading? */
> int modules_disabled = 0;
> diff --git a/kernel/printk.c b/kernel/printk.c
> index 1751c45..d86c91a 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -420,6 +420,22 @@ SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
> return do_syslog(type, buf, len);
> }
>
> +#ifdef CONFIG_KGDB_KDB
> +/* kdb dmesg command needs access to the syslog buffer. do_syslog()
> + * uses locks so it cannot be used during debugging. Just tell kdb
> + * where the start and end of the physical and logical logs are. This
> + * is equivalent to do_syslog(3).
> + */
> +void kdb_syslog_data(char *syslog_data[4])
> +{
> + syslog_data[0] = log_buf;
> + syslog_data[1] = log_buf + log_buf_len;
> + syslog_data[2] = log_buf + log_end -
> + (logged_chars < log_buf_len ? logged_chars : log_buf_len);
> + syslog_data[3] = log_buf + log_end;
> +}
> +#endif /* CONFIG_KGDB_KDB */
> +
> /*
> * Call the console drivers on a range of log_buf
> */
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 3a8fb30..92ab8b8 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -9802,9 +9802,9 @@ void normalize_rt_tasks(void)
>
> #endif /* CONFIG_MAGIC_SYSRQ */
>
> -#ifdef CONFIG_IA64
> +#if defined(CONFIG_IA64) || defined(CONFIG_KGDB_KDB)
> /*
> - * These functions are only useful for the IA64 MCA handling.
> + * These functions are only useful for the IA64 MCA handling, or kdb.
> *
> * They can only be called when the whole system has been
> * stopped - every CPU needs to be quiescent, and no scheduling
> @@ -9824,6 +9824,9 @@ struct task_struct *curr_task(int cpu)
> return cpu_curr(cpu);
> }
>
> +#endif /* defined(CONFIG_IA64) || defined(CONFIG_KGDB_KDB) */
> +
> +#ifdef CONFIG_IA64
> /**
> * set_curr_task - set the current task for a given cpu.
> * @cpu: the processor in question.
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 934ae5e..96ecbf8 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2718,3 +2718,43 @@ void __init signals_init(void)
> {
> sigqueue_cachep = KMEM_CACHE(sigqueue, SLAB_PANIC);
> }
> +
> +#ifdef CONFIG_KGDB_KDB
> +#include <linux/kdb.h>
> +/*
> + * kdb_send_sig_info - Allows kdb to send signals without exposing
> + * signal internals. This function checks if the required locks are
> + * available before calling the main signal code, to avoid kdb
> + * deadlocks.
> + */
> +void
> +kdb_send_sig_info(struct task_struct *t, struct siginfo *info)
> +{
> + static struct task_struct *kdb_prev_t;
> + int sig, new_t;
> + if (!spin_trylock(&t->sighand->siglock)) {
> + kdb_printf("Can't do kill command now.\n"
> + "The sigmask lock is held somewhere else in "
> + "kernel, try again later\n");
> + return;
> + }
> + spin_unlock(&t->sighand->siglock);
> + new_t = kdb_prev_t != t;
> + kdb_prev_t = t;
> + if (t->state != TASK_RUNNING && new_t) {
> + kdb_printf("Process is not RUNNING, sending a signal from "
> + "kdb risks deadlock\n"
> + "on the run queue locks. "
> + "The signal has _not_ been sent.\n"
> + "Reissue the kill command if you want to risk "
> + "the deadlock.\n");
> + return;
> + }
> + sig = info->si_signo;
> + if (send_sig_info(sig, info, t))
> + kdb_printf("Fail to deliver Signal %d to process %d.\n",
> + sig, t->pid);
> + else
> + kdb_printf("Signal %d is sent to process %d.\n", sig, t->pid);
> +}
> +#endif /* CONFIG_KGDB_KDB */
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 6c0585b..dc2039e 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -13,6 +13,7 @@
> #include <linux/swap.h>
> #include <linux/vmalloc.h>
> #include <linux/pagemap.h>
> +#include <linux/kdb.h>
> #include <linux/namei.h>
> #include <linux/shm.h>
> #include <linux/blkdev.h>
> @@ -2056,12 +2057,11 @@ out:
> return error;
> }
>
> -void si_swapinfo(struct sysinfo *val)
> +void __si_swapinfo(struct sysinfo *val)
> {
> unsigned int type;
> unsigned long nr_to_be_unused = 0;
>
> - spin_lock(&swap_lock);
> for (type = 0; type < nr_swapfiles; type++) {
> struct swap_info_struct *si = swap_info[type];
>
> @@ -2070,6 +2070,12 @@ void si_swapinfo(struct sysinfo *val)
> }
> val->freeswap = nr_swap_pages + nr_to_be_unused;
> val->totalswap = total_swap_pages + nr_to_be_unused;
> +}
> +
> +void si_swapinfo(struct sysinfo *val)
> +{
> + spin_lock(&swap_lock);
> + __si_swapinfo(val);
> spin_unlock(&swap_lock);
> }
>
> --
> 1.6.4.rc1
>
> --
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