Maybe something like this might be a useful debug option to detect unwise likely()/unlikely() usage?
This is a quick hack (not submitted for inclusion), but it works on my box and detected certain points after boot. Anyone likes this idea?
The reason I had to add printk_debug_likely() is that using printk directly gives compile error. It seems not to like asmlinkage for some reason..I guess likely/unlikely are too fundamental macros and the dependency gets too messy. Or maybe it could be fixed in a way I've not found.
It increases kernel size by about 10%, but hey, it's a debugg option. :-)
Sample print:
possible (un)likely misuse at include/asm/mmu_context.h:32/switch_mm()
<c011b644> printk_debug_likely+0x25/0x31 <c02b3092> schedule+0xb04/0xefa
<c02b457b> __mutex_lock_slowpath+0x35a/0x89e <c016c0fd> real_lookup+0x1f/0xb3
<c016c0fd> real_lookup+0x1f/0xb3 <c016c512> do_lookup+0x50/0xe8
<c016d14b> __link_path_walk+0xba1/0x125f <c016d8a6> link_path_walk+0x9d/0x166
<c014b911> __handle_mm_fault+0x2fd/0x35b <c01ca29e> _atomic_dec_and_lock+0x22/0x2c
<c016d5c2> __link_path_walk+0x1018/0x125f <c016d8a6> link_path_walk+0x9d/0x166
<c014b911> __handle_mm_fault+0x2fd/0x35b <c01ce9fe> strncpy_from_user+0x94/0xb3
<c016dee7> do_path_lookup+0x35c/0x4d2 <c016e385> __user_walk_fd+0x84/0x9b
<c0167ae1> vfs_stat_fd+0x15/0x3c <c014b911> __handle_mm_fault+0x2fd/0x35b
<c0168091> sys_stat64+0xf/0x23 <c0113fea> do_page_fault+0x30d/0x753
<c01ceefd> copy_to_user+0x113/0x11c <c0126ee6> sys_rt_sigprocmask+0xae/0xc1
<c01035cb> sysenter_past_esp+0x54/0x75
possible (un)likely misuse at kernel/sched.c:1638/context_switch()
<c011b644> printk_debug_likely+0x25/0x31 <c02b3025> schedule+0xa97/0xefa
<c011ddcd> do_exit+0x75b/0x765 <c011dec4> sys_exit_group+0x0/0xd
<c01035cb> sysenter_past_esp+0x54/0x75
possible (un)likely misuse at kernel/softlockup.c:59/softlockup_tick()
<c011b644> printk_debug_likely+0x25/0x31 <c0138f78> softlockup_tick+0x88/0xf5
<c0123dcd> update_process_times+0x35/0x57 <c0106133> timer_interrupt+0x3d/0x60
<c013919c> handle_IRQ_event+0x21/0x4a <c01392f7> __do_IRQ+0x132/0x1e7
<c0104d86> do_IRQ+0x9c/0xab <c01037fe> common_interrupt+0x1a/0x20
possible (un)likely misuse at kernel/sched.c:1645/context_switch()
<c011b644> printk_debug_likely+0x25/0x31 <c02b3236> schedule+0xca8/0xefa
<c0130d33> enqueue_hrtimer+0x5b/0x80 <c02b57f5> do_nanosleep+0x3b/0xc0
<c0131092> hrtimer_nanosleep+0x45/0xe6 <c01680b4> sys_lstat64+0xf/0x23
<c013102a> hrtimer_wakeup+0x0/0x18 <c01cf021> copy_from_user+0x11b/0x142
<c0131179> sys_nanosleep+0x46/0x4e <c01035cb> sysenter_past_esp+0x54/0x75
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index f23d3c6..a6df5f7 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -58,9 +58,32 @@ #endif
* build go below this comment. Actual compiler/compiler version
* specific implementations come from the above header files
*/
+#define CONFIG_DEBUG_LIKELY
+#ifdef CONFIG_DEBUG_LIKELY
+extern int printk_debug_likely(const char *fmt, ...);
+extern int debug_likely_count_min_thresh;
+extern int debug_likely_print_max_thresh;
+#define __check_likely(x, v, uv) \
+ ({ static int _ckl_print_nr = 0; \
+ static unsigned int _ckl_s[2]; \
+ int _ckl_r = !!(x); \
+ _ckl_s[_ckl_r]++; \
+ if ((_ckl_s[v] == _ckl_s[uv]) && (_ckl_s[v] > debug_likely_count_min_thresh) \
+ && (_ckl_print_nr < debug_likely_print_max_thresh)) { \
+ _ckl_print_nr++; \
+ printk_debug_likely("possible (un)likely misuse at %s:%d/%s()\n", \
+ __FILE__, __LINE__, __FUNCTION__); \
+ } \
+ _ckl_r; })
+#else
+#define __check_likely(x, v, uv) __builtin_expect(!!(x), v)
+#endif
+
+#define likely(x) __check_likely(x, 1, 0)
+#define unlikely(x) __check_likely(x, 0, 1)
-#define likely(x) __builtin_expect(!!(x), 1)
-#define unlikely(x) __builtin_expect(!!(x), 0)
+//#define likely(x) __builtin_expect(!!(x), 1)
+//#define unlikely(x) __builtin_expect(!!(x), 0)
/* Optimization barrier */
#ifndef barrier
diff --git a/kernel/printk.c b/kernel/printk.c
index c056f33..cc09dca 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -602,6 +602,30 @@ out:
EXPORT_SYMBOL(printk);
EXPORT_SYMBOL(vprintk);
+#ifdef CONFIG_DEBUG_LIKELY
+int debug_likely_count_min_thresh = 100;
+int debug_likely_print_max_thresh = 1;
+int printk_debug_likely(const char *fmt, ...)
+{
+ int r = 0;
+ static atomic_t recurse = ATOMIC_INIT(1); /* as a mutex */
+ if (atomic_dec_and_test(&recurse)) {
+ va_list args;
+
+ va_start(args, fmt);
+ r = vprintk(fmt, args);
+ va_end(args);
+ dump_stack();
+ }
+ atomic_inc(&recurse);
+
+ return r;
+}
+EXPORT_SYMBOL(debug_likely_count_min_thresh);
+EXPORT_SYMBOL(debug_likely_print_max_thresh);
+EXPORT_SYMBOL(printk_debug_likely);
+#endif
+
#else
asmlinkage long sys_syslog(int type, char __user *buf, int len)
-
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