From: Andrew Morton <andrewm@uow.edu.au>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: [patch] remove oops->printk deadlock
Date: Sat, 18 Nov 2000 14:51:43 +1100 [thread overview]
Message-ID: <3A15FCCF.C2666BAD@uow.edu.au> (raw)
Linus,
patch removes the last deadlock opportunity in the x86 oops and
NMI oopser path, namely the call to wake_up_interruptible()
within printk itself. (Apart from vga_lock, which isn't
worth the fuss).
bust_spinlocks() disappears again in favour of a global integer
`oops_in_progress'.
I've only reviewed the vt_console device talking to vgacon. Other
console devices almost certainly have deadlock opportunities. They're
easy to fix:
+ if (oops_in_progress)
+ spin_lock_init(&some_lock); /* Sorry, George */
spin_lock(&some_lock);
Other SMP-capable architectures may simply set and clear
oops_in_progress at the appropriate times.
poke_blanked_console() can come back if we want. Just don't
call it if oops_in_progress is true.
--- linux-2.4.0-test11-pre4/include/linux/kernel.h Sun Oct 15 01:27:46 2000
+++ linux-akpm/include/linux/kernel.h Mon Nov 13 19:44:58 2000
@@ -62,6 +62,7 @@
asmlinkage int printk(const char * fmt, ...)
__attribute__ ((format (printf, 1, 2)));
+extern int oops_in_progress;
#if DEBUG
#define pr_debug(fmt,arg...) \
--- linux-2.4.0-test11-pre4/kernel/printk.c Sat Nov 4 16:22:49 2000
+++ linux-akpm/kernel/printk.c Mon Nov 13 19:58:36 2000
@@ -51,6 +51,7 @@
static unsigned long logged_chars;
struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
static int preferred_console = -1;
+int oops_in_progress;
/*
* Setup a list of consoles. Called from init/main.c
@@ -260,6 +261,8 @@
static signed char msg_level = -1;
long flags;
+ if (oops_in_progress)
+ spin_lock_init(&console_lock);
spin_lock_irqsave(&console_lock, flags);
va_start(args, fmt);
i = vsprintf(buf + 3, fmt, args); /* hopefully i < sizeof(buf)-4 */
@@ -308,7 +311,8 @@
msg_level = -1;
}
spin_unlock_irqrestore(&console_lock, flags);
- wake_up_interruptible(&log_wait);
+ if (!oops_in_progress)
+ wake_up_interruptible(&log_wait);
return i;
}
--- linux-2.4.0-test11-pre4/arch/i386/mm/fault.c Mon Nov 13 18:23:49 2000
+++ linux-akpm/arch/i386/mm/fault.c Mon Nov 13 19:44:58 2000
@@ -77,19 +77,6 @@
return 0;
}
-extern spinlock_t console_lock, timerlist_lock;
-
-/*
- * Unlock any spinlocks which will prevent us from getting the
- * message out (timerlist_lock is aquired through the
- * console unblank code)
- */
-void bust_spinlocks(void)
-{
- spin_lock_init(&console_lock);
- spin_lock_init(&timerlist_lock);
-}
-
asmlinkage void do_invalid_op(struct pt_regs *, unsigned long);
extern unsigned long idt;
@@ -264,8 +251,7 @@
* terminate things with extreme prejudice.
*/
- bust_spinlocks();
-
+ oops_in_progress = 1;
if (address < PAGE_SIZE)
printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
else
@@ -283,6 +269,7 @@
printk(KERN_ALERT "*pte = %08lx\n", page);
}
die("Oops", regs, error_code);
+ oops_in_progress = 0;
do_exit(SIGKILL);
/*
--- linux-2.4.0-test11-pre4/arch/i386/kernel/traps.c Mon Nov 13 18:23:49 2000
+++ linux-akpm/arch/i386/kernel/traps.c Mon Nov 13 19:44:58 2000
@@ -63,7 +63,6 @@
struct desc_struct idt_table[256] __attribute__((__section__(".data.idt"))) = { {0, 0}, };
extern int console_loglevel;
-extern void bust_spinlocks(void);
static inline void console_silent(void)
{
@@ -437,12 +436,13 @@
* We are in trouble anyway, lets at least try
* to get a message out.
*/
- bust_spinlocks();
+ oops_in_progress = 1;
printk("NMI Watchdog detected LOCKUP on CPU%d, registers:\n", cpu);
show_registers(regs);
printk("console shuts up ...\n");
console_silent();
spin_unlock(&nmi_print_lock);
+ oops_in_progress = 0;
do_exit(SIGSEGV);
}
} else {
-
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