Subject: + printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch added to -mm tree
To: jack@xxxxxxx,fweisbec@xxxxxxxxx,pmladek@xxxxxxx,rostedt@xxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Thu, 13 Mar 2014 16:14:42 -0700
The patch titled
Subject: printk: release lockbuf_lock before calling console_trylock_for_printk()
has been added to the -mm tree. Its filename is
printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: printk: release lockbuf_lock before calling console_trylock_for_printk()
There's no reason to hold lockbuf_lock when entering
console_trylock_for_printk(). The first thing this function does is
calling down_trylock(console_sem) and if that fails it immediately unlocks
lockbuf_lock. So lockbuf_lock isn't needed for that branch. When
down_trylock() succeeds, the rest of console_trylock() is OK without
lockbuf_lock (it is called without it from other places), and the only
remaining thing in console_trylock_for_printk() is can_use_console() call.
For that call console_sem is enough (it iterates all consoles and checks
CON_ANYTIME flag).
So we drop logbuf_lock before entering console_trylock_for_printk() which
simplifies the code.
Signed-off-by: Jan Kara <jack@xxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/printk/printk.c | 49 +++++++++++++--------------------------
1 file changed, 17 insertions(+), 32 deletions(-)
diff -puN kernel/printk/printk.c~printk-release-lockbuf_lock-before-calling-console_trylock_for_printk kernel/printk/printk.c
--- a/kernel/printk/printk.c~printk-release-lockbuf_lock-before-calling-console_trylock_for_printk
+++ a/kernel/printk/printk.c
@@ -249,9 +249,6 @@ static char __log_buf[__LOG_BUF_LEN] __a
static char *log_buf = __log_buf;
static u32 log_buf_len = __LOG_BUF_LEN;
-/* cpu currently holding logbuf_lock */
-static volatile unsigned int logbuf_cpu = UINT_MAX;
-
/* human readable text of the record */
static char *log_text(const struct printk_log *msg)
{
@@ -1332,36 +1329,22 @@ static inline int can_use_console(unsign
* messages from a 'printk'. Return true (and with the
* console_lock held, and 'console_locked' set) if it
* is successful, false otherwise.
- *
- * This gets called with the 'logbuf_lock' spinlock held and
- * interrupts disabled. It should return with 'lockbuf_lock'
- * released but interrupts still disabled.
*/
static int console_trylock_for_printk(unsigned int cpu)
- __releases(&logbuf_lock)
{
- int retval = 0, wake = 0;
-
- if (console_trylock()) {
- retval = 1;
-
- /*
- * If we can't use the console, we need to release
- * the console semaphore by hand to avoid flushing
- * the buffer. We need to hold the console semaphore
- * in order to do this test safely.
- */
- if (!can_use_console(cpu)) {
- console_locked = 0;
- wake = 1;
- retval = 0;
- }
- }
- logbuf_cpu = UINT_MAX;
- raw_spin_unlock(&logbuf_lock);
- if (wake)
+ if (!console_trylock())
+ return 0;
+ /*
+ * If we can't use the console, we need to release the console
+ * semaphore by hand to avoid flushing the buffer. We need to hold the
+ * console semaphore in order to do this test safely.
+ */
+ if (!can_use_console(cpu)) {
+ console_locked = 0;
up(&console_sem);
- return retval;
+ return 0;
+ }
+ return 1;
}
int printk_delay_msec __read_mostly;
@@ -1494,6 +1477,9 @@ asmlinkage int vprintk_emit(int facility
unsigned long flags;
int this_cpu;
int printed_len = 0;
+ /* cpu currently holding logbuf_lock in this function */
+ static volatile unsigned int logbuf_cpu = UINT_MAX;
+
boot_delay_msec(level);
printk_delay();
@@ -1612,13 +1598,12 @@ asmlinkage int vprintk_emit(int facility
}
printed_len += text_len;
+ logbuf_cpu = UINT_MAX;
+ raw_spin_unlock(&logbuf_lock);
/*
* Try to acquire and then immediately release the console semaphore.
* The release will print out buffers and wake up /dev/kmsg and syslog()
* users.
- *
- * The console_trylock_for_printk() function will release 'logbuf_lock'
- * regardless of whether it actually gets the console semaphore or not.
*/
if (console_trylock_for_printk(this_cpu))
console_unlock();
_
Patches currently in -mm which might be from jack@xxxxxxx are
backing_dev-fix-hung-task-on-sync.patch
backing_dev-fix-hung-task-on-sync-fix.patch
bdi-avoid-oops-on-device-removal.patch
kthread-ensure-locality-of-task_struct-allocations.patch
fanotify-remove-useless-bypass_perm-check.patch
fanotify-use-fanotify-event-structure-for-permission-response-processing.patch
fanotify-convert-access_mutex-to-spinlock.patch
fanotify-reorganize-loop-in-fanotify_read.patch
fanotify-move-unrelated-handling-from-copy_event_to_user.patch
ocfs2-remove-ocfs2_inode_skip_delete-flag.patch
ocfs2-move-dquot_initialize-in-ocfs2_delete_inode-somewhat-later.patch
quota-provide-function-to-grab-quota-structure-reference.patch
ocfs2-implement-delayed-dropping-of-last-dquot-reference.patch
ocfs2-avoid-blocking-in-ocfs2_mark_lockres_freeing-in-downconvert-thread.patch
ocfs2-revert-iput-deferring-code-in-ocfs2_drop_dentry_lock.patch
mm-vmstat-fix-up-zone-state-accounting.patch
fs-cachefiles-use-add_to_page_cache_lru.patch
lib-radix-tree-radix_tree_delete_item.patch
mm-shmem-save-one-radix-tree-lookup-when-truncating-swapped-pages.patch
mm-filemap-move-radix-tree-hole-searching-here.patch
mm-fs-prepare-for-non-page-entries-in-page-cache-radix-trees.patch
mm-fs-store-shadow-entries-in-page-cache.patch
mm-thrash-detection-based-file-cache-sizing.patch
lib-radix_tree-tree-node-interface.patch
mm-keep-page-cache-radix-tree-nodes-in-check.patch
mm-readaheadc-fix-readahead-failure-for-memoryless-numa-nodes-and-limit-readahead-pages.patch
fs-mpagec-forgotten-write_sync-in-case-of-data-integrity-write.patch
printk-remove-duplicated-check-for-log-level.patch
printk-remove-obsolete-check-for-log-level-c.patch
printk-add-comment-about-tricky-check-for-text-buffer-size.patch
printk-use-also-the-last-bytes-in-the-ring-buffer.patch
printk-do-not-compute-the-size-of-the-message-twice.patch
printk-remove-outdated-comment.patch
printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
printk-enable-interrupts-before-calling-console_trylock_for_printk.patch
printk-remove-separate-printk_sched-buffers-and-use-printk-buf-instead.patch
printk-hand-over-printing-to-console-if-printing-too-long.patch
kernel-avoid-softlockups-in-stop_machine-during-heavy-printing.patch
linux-next.patch
mm-add-strictlimit-knob-v2.patch
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