+ buffer_head-remove-redundant-test-from-wait_on_buffer-fix.patch added to -mm tree

+ buffer_head-remove-redundant-test-from-wait_on_buffer-fix.patch added to -mm tree

[akpm]

The patch titled
     buffer_head-remove-redundant-test-from-wait_on_buffer-fix
has been added to the -mm tree.  Its filename is
     buffer_head-remove-redundant-test-from-wait_on_buffer-fix.patch

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out what to do about this

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------------------------------------------------------
Subject: buffer_head-remove-redundant-test-from-wait_on_buffer-fix
From: Andrew Morton <akpm@linux-foundation.org>

restore the test

Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Richard Kennedy <richard@rsk.demon.co.uk>
Cc: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/buffer.c                 |    6 ++++++
 include/linux/buffer_head.h |    7 ++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff -puN fs/buffer.c~buffer_head-remove-redundant-test-from-wait_on_buffer-fix fs/buffer.c
--- a/fs/buffer.c~buffer_head-remove-redundant-test-from-wait_on_buffer-fix
+++ a/fs/buffer.c
@@ -90,6 +90,12 @@ EXPORT_SYMBOL(unlock_buffer);
  */
 void __wait_on_buffer(struct buffer_head * bh)
 {
+	/*
+	 * Calling wait_on_buffer() against a zero-ref buffer is a nasty bug
+	 * because it will almost always "work".  However this buffer can be
+	 * reclaimed at any time.  So check for it.
+	 */
+	VM_BUG_ON(atomic_read(&bh->b_count) == 0);
 	wait_on_bit(&bh->b_state, BH_Lock, sync_buffer, TASK_UNINTERRUPTIBLE);
 }
 EXPORT_SYMBOL(__wait_on_buffer);
diff -puN include/linux/buffer_head.h~buffer_head-remove-redundant-test-from-wait_on_buffer-fix include/linux/buffer_head.h
--- a/include/linux/buffer_head.h~buffer_head-remove-redundant-test-from-wait_on_buffer-fix
+++ a/include/linux/buffer_head.h
@@ -305,10 +305,15 @@ map_bh(struct buffer_head *bh, struct su
 	bh->b_size = sb->s_blocksize;
 }
 
+/*
+ * Calling wait_on_buffer() for a zero-ref buffer is illegal, so we call into
+ * __wait_on_buffer() just to trip a debug check.  Because debug code in inline
+ * functions is bloaty.
+ */
 static inline void wait_on_buffer(struct buffer_head *bh)
 {
 	might_sleep();
-	if (buffer_locked(bh))
+	if (buffer_locked(bh) || atomic_read(&bh->b_count) == 0)
 		__wait_on_buffer(bh);
 }
 
_

Patches currently in -mm which might be from akpm@linux-foundation.org are

origin.patch
linux-next.patch
next-remove-localversion.patch
i-need-old-gcc.patch
arch-x86-crypto-aesni-intel_asms-still-busted.patch
include-linux-fsh-complete-hexification-of-fmode_-constants.patch
drivers-video-efifbc-framebuffer-for-nvidia-9400m-in-macbook-pro-51-fix.patch
intel-agpc-fix-crash-when-accessing-nonexistent-gtt-entries-in-i915-checkpatch-fixes.patch
iio-iio_get_new_idr_val-return-negative-value-on-failure-fix.patch
drivers-acpi-use-kasprintf-fix.patch
acpi_pad-processor_aggregator-name-too-long-fix.patch
arch-arm-include-asm-elfh-forward-declare-the-task-struct.patch
cifs-provide-user-with-a-hint-when-name-resolution-fails-fix.patch
jfs-free-sbi-memory-in-error-path.patch
fs-fscache-object-listc-fix-warning-on-32-bit.patch
of-gpio-implement-gpiolib-notifier-hooks-fix.patch
of-gpio-implement-gpiolib-notifier-hooks-fix-fix2.patch
hpet-factor-timer-allocate-from-open-fix.patch
led-driver-for-the-soekris-net5501-board-checkpatch-fixes.patch
leds-route-kbd-leds-through-the-generic-leds-layer-fix.patch
gpio-add-support-for-janz-vmod-ttl-digital-io-module-fix.patch
3x59x-fix-pci-resource-management.patch
backlight-add-s6e63m0-amoled-lcd-panel-driver-checkpatch-fixes.patch
serial-timbuart-make-sure-last-byte-is-sent-when-port-is-closed-fix.patch
kernel-irq-managec-add-raise_threaded_irq-fix.patch
max3100-to_max3100_port-small-style-fixes-fix.patch
mm-export-unusable-free-space-index-via-proc-unusable_index-fix-fix-2.patch
mm-compaction-direct-compact-when-a-high-order-allocation-fails-reject-fix.patch
vmstat-fix-build-errors-when-proc_fs-is-disabled-checkpatch-fixes.patch
mm-compaction-do-not-display-compaction-related-stats-when-config_compaction-fix.patch
mm-compaction-do-not-display-compaction-related-stats-when-config_compaction-fix-fix-2.patch
buffer_head-remove-redundant-test-from-wait_on_buffer-fix.patch
wait_on_buffer-remove-the-buffer_locked-test.patch
frv-extend-gdbstub-to-support-more-features-of-gdb-fix.patch
frv-duplicate-output_buffer-of-e03-checkpatch-fixes.patch
kernel-wide-replace-ushort_max-short_max-and-short_min-with-ushrt_max-shrt_max-and-shrt_min-fix.patch
firmware-loader-use-statically-initialized-data-attribute-fix.patch
firmware-loader-use-statically-initialized-data-attribute-fix-fix.patch
davinci-mmc-updates-to-suspend-resume-implementation-checkpatch-fixes.patch
checkpatch-add-check-for-too-short-kconfig-descriptions-checkpatch-fixes.patch
hwmon-driver-for-ti-tmp102-temperature-sensor.patch
hwmon-driver-for-ti-tmp102-temperature-sensor-fix.patch
hwmon-add-ti-ads7871-a-d-converter-driver-checkpatch-fixes.patch
rtc-mxc-remove-unnecessary-clock-source-for-rtc-subsystem.patch
gpiolib-make-names-array-and-its-values-const-fix.patch
memcg-oom-kill-disable-and-oom-status-update-checkpatch-fixes.patch
memcg-move-charge-of-file-pages-fix.patch
proc-turn-signal_struct-count-into-int-nr_threads-checkpatch-fixes.patch
fault-injection-add-cpu-notifier-error-injection-module-fix.patch
delay-accounting-re-implement-c-for-getdelaysc-to-report-information-on-a-target-command-checkpatch-fixes.patch
panic-allow-taint-flag-for-warnings-to-be-changed-from-taint_warn-checkpatch-fixes.patch
x86_32-use-asm-generic-scatterlisth.patch
reiser4-export-remove_from_page_cache-fix.patch
reiser4.patch
reiser4-writeback_inodes-implementation-fix.patch
reiser4-fixups.patch
reiser4-broke.patch
slab-leaks3-default-y.patch
put_bh-debug.patch
getblk-handle-2tb-devices.patch
getblk-handle-2tb-devices-fix.patch
notify_change-callers-must-hold-i_mutex.patch