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![Guilherme G. Piccoli](/assets/img/avatar_default.png)
Currently many console drivers for s390 rely on panic/reboot notifiers to invoke callbacks on these events. The panic() function disables local IRQs, secondary CPUs and preemption, so callbacks invoked on panic are effectively running in atomic context. Happens that most of these console callbacks from s390 doesn't take the proper care with regards to atomic context, like taking spinlocks that might be taken in other function/CPU and hence will cause a lockup situation. The goal for this patch is to improve the notifiers reliability, acting on 4 console drivers, as detailed below: (1) con3215: changed a regular spinlock to the trylock alternative. (2) con3270: also changed a regular spinlock to its trylock counterpart, but here we also have another problem: raw3270_activate_view() takes a different spinlock. So, we worked a helper to validate if this other lock is safe to acquire, and if so, raw3270_activate_view() should be safe. Notice though that there is a functional change here: it's now possible to continue the notifier code [reaching con3270_wait_write() and con3270_rebuild_update()] without executing raw3270_activate_view(). (3) sclp: a global lock is used heavily in the functions called from the notifier, so we added a check here - if the lock is taken already, we just bail-out, preventing the lockup. (4) sclp_vt220: same as (3), a lock validation was added to prevent the potential lockup problem. Besides (1)-(4), we also removed useless void functions, adding the code called from the notifier inside its own body, and changed the priority of such notifiers to execute late, since they are "heavyweight" for the panic environment, so we aim to reduce risks here. Changed return values to NOTIFY_DONE as well, the standard one. Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com> Link: https://lore.kernel.org/r/20220427224924.592546-14-gpiccoli@igalia.com Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
297 lines
7.5 KiB
C
297 lines
7.5 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* SCLP line mode console driver
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*
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* Copyright IBM Corp. 1999, 2009
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* Author(s): Martin Peschke <mpeschke@de.ibm.com>
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* Martin Schwidefsky <schwidefsky@de.ibm.com>
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*/
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#include <linux/kmod.h>
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#include <linux/console.h>
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#include <linux/init.h>
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#include <linux/panic_notifier.h>
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#include <linux/timer.h>
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#include <linux/jiffies.h>
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#include <linux/termios.h>
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#include <linux/err.h>
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#include <linux/reboot.h>
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#include <linux/gfp.h>
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#include "sclp.h"
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#include "sclp_rw.h"
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#include "sclp_tty.h"
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#define sclp_console_major 4 /* TTYAUX_MAJOR */
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#define sclp_console_minor 64
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#define sclp_console_name "ttyS"
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/* Lock to guard over changes to global variables */
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static DEFINE_SPINLOCK(sclp_con_lock);
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/* List of free pages that can be used for console output buffering */
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static LIST_HEAD(sclp_con_pages);
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/* List of full struct sclp_buffer structures ready for output */
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static LIST_HEAD(sclp_con_outqueue);
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/* Pointer to current console buffer */
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static struct sclp_buffer *sclp_conbuf;
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/* Timer for delayed output of console messages */
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static struct timer_list sclp_con_timer;
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/* Flag that output queue is currently running */
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static int sclp_con_queue_running;
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/* Output format for console messages */
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#define SCLP_CON_COLUMNS 320
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#define SPACES_PER_TAB 8
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static void
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sclp_conbuf_callback(struct sclp_buffer *buffer, int rc)
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{
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unsigned long flags;
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void *page;
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do {
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page = sclp_unmake_buffer(buffer);
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spin_lock_irqsave(&sclp_con_lock, flags);
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/* Remove buffer from outqueue */
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list_del(&buffer->list);
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list_add_tail((struct list_head *) page, &sclp_con_pages);
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/* Check if there is a pending buffer on the out queue. */
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buffer = NULL;
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if (!list_empty(&sclp_con_outqueue))
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buffer = list_first_entry(&sclp_con_outqueue,
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struct sclp_buffer, list);
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if (!buffer) {
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sclp_con_queue_running = 0;
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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break;
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}
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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} while (sclp_emit_buffer(buffer, sclp_conbuf_callback));
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}
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/*
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* Finalize and emit first pending buffer.
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*/
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static void sclp_conbuf_emit(void)
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{
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struct sclp_buffer* buffer;
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unsigned long flags;
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int rc;
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spin_lock_irqsave(&sclp_con_lock, flags);
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if (sclp_conbuf)
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list_add_tail(&sclp_conbuf->list, &sclp_con_outqueue);
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sclp_conbuf = NULL;
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if (sclp_con_queue_running)
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goto out_unlock;
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if (list_empty(&sclp_con_outqueue))
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goto out_unlock;
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buffer = list_first_entry(&sclp_con_outqueue, struct sclp_buffer,
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list);
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sclp_con_queue_running = 1;
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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rc = sclp_emit_buffer(buffer, sclp_conbuf_callback);
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if (rc)
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sclp_conbuf_callback(buffer, rc);
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return;
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out_unlock:
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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}
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/*
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* Wait until out queue is empty
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*/
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static void sclp_console_sync_queue(void)
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{
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unsigned long flags;
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spin_lock_irqsave(&sclp_con_lock, flags);
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del_timer(&sclp_con_timer);
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while (sclp_con_queue_running) {
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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sclp_sync_wait();
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spin_lock_irqsave(&sclp_con_lock, flags);
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}
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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}
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/*
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* When this routine is called from the timer then we flush the
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* temporary write buffer without further waiting on a final new line.
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*/
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static void
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sclp_console_timeout(struct timer_list *unused)
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{
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sclp_conbuf_emit();
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}
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/*
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* Drop oldest console buffer if sclp_con_drop is set
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*/
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static int
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sclp_console_drop_buffer(void)
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{
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struct list_head *list;
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struct sclp_buffer *buffer;
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void *page;
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if (!sclp_console_drop)
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return 0;
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list = sclp_con_outqueue.next;
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if (sclp_con_queue_running)
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/* The first element is in I/O */
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list = list->next;
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if (list == &sclp_con_outqueue)
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return 0;
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list_del(list);
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buffer = list_entry(list, struct sclp_buffer, list);
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page = sclp_unmake_buffer(buffer);
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list_add_tail((struct list_head *) page, &sclp_con_pages);
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return 1;
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}
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/*
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* Writes the given message to S390 system console
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*/
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static void
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sclp_console_write(struct console *console, const char *message,
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unsigned int count)
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{
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unsigned long flags;
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void *page;
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int written;
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if (count == 0)
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return;
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spin_lock_irqsave(&sclp_con_lock, flags);
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/*
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* process escape characters, write message into buffer,
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* send buffer to SCLP
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*/
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do {
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/* make sure we have a console output buffer */
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if (sclp_conbuf == NULL) {
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if (list_empty(&sclp_con_pages))
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sclp_console_full++;
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while (list_empty(&sclp_con_pages)) {
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if (sclp_console_drop_buffer())
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break;
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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sclp_sync_wait();
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spin_lock_irqsave(&sclp_con_lock, flags);
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}
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page = sclp_con_pages.next;
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list_del((struct list_head *) page);
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sclp_conbuf = sclp_make_buffer(page, SCLP_CON_COLUMNS,
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SPACES_PER_TAB);
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}
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/* try to write the string to the current output buffer */
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written = sclp_write(sclp_conbuf, (const unsigned char *)
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message, count);
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if (written == count)
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break;
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/*
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* Not all characters could be written to the current
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* output buffer. Emit the buffer, create a new buffer
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* and then output the rest of the string.
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*/
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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sclp_conbuf_emit();
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spin_lock_irqsave(&sclp_con_lock, flags);
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message += written;
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count -= written;
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} while (count > 0);
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/* Setup timer to output current console buffer after 1/10 second */
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if (sclp_conbuf != NULL && sclp_chars_in_buffer(sclp_conbuf) != 0 &&
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!timer_pending(&sclp_con_timer)) {
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mod_timer(&sclp_con_timer, jiffies + HZ / 10);
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}
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spin_unlock_irqrestore(&sclp_con_lock, flags);
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}
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static struct tty_driver *
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sclp_console_device(struct console *c, int *index)
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{
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*index = c->index;
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return sclp_tty_driver;
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}
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/*
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* This panic/reboot notifier makes sure that all buffers
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* will be flushed to the SCLP.
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*/
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static int sclp_console_notify(struct notifier_block *self,
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unsigned long event, void *data)
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{
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/*
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* Perform the lock check before effectively getting the
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* lock on sclp_conbuf_emit() / sclp_console_sync_queue()
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* to prevent potential lockups in atomic context.
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*/
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if (spin_is_locked(&sclp_con_lock))
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return NOTIFY_DONE;
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sclp_conbuf_emit();
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sclp_console_sync_queue();
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return NOTIFY_DONE;
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}
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static struct notifier_block on_panic_nb = {
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.notifier_call = sclp_console_notify,
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.priority = INT_MIN + 1, /* run the callback late */
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};
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static struct notifier_block on_reboot_nb = {
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.notifier_call = sclp_console_notify,
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.priority = INT_MIN + 1, /* run the callback late */
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};
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/*
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* used to register the SCLP console to the kernel and to
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* give printk necessary information
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*/
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static struct console sclp_console =
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{
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.name = sclp_console_name,
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.write = sclp_console_write,
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.device = sclp_console_device,
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.flags = CON_PRINTBUFFER,
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.index = 0 /* ttyS0 */
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};
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/*
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* called by console_init() in drivers/char/tty_io.c at boot-time.
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*/
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static int __init
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sclp_console_init(void)
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{
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void *page;
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int i;
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int rc;
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/* SCLP consoles are handled together */
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if (!(CONSOLE_IS_SCLP || CONSOLE_IS_VT220))
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return 0;
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rc = sclp_rw_init();
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if (rc)
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return rc;
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/* Allocate pages for output buffering */
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for (i = 0; i < sclp_console_pages; i++) {
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page = (void *) get_zeroed_page(GFP_KERNEL | GFP_DMA);
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list_add_tail(page, &sclp_con_pages);
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}
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sclp_conbuf = NULL;
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timer_setup(&sclp_con_timer, sclp_console_timeout, 0);
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/* enable printk-access to this driver */
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atomic_notifier_chain_register(&panic_notifier_list, &on_panic_nb);
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register_reboot_notifier(&on_reboot_nb);
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register_console(&sclp_console);
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return 0;
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}
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console_initcall(sclp_console_init);
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