工作顺利
by 米英秀
问题的发现、分析与解决
课程设计逻辑
在工作中，会遇到各种各样的问题，如何有效解决和杜绝这些问题，就变成了每一个职场高手的必修课。
1.如何抓住问题解决的本质？
2.如何早期发现、干预或杜绝问题？
3.如何有效的分析问题的根本原因？
4.如何使用简单、高效的方法解决问题？
5.如何避免问题的重复发生？
本课程将带着这些问题，透过现象看本质的追根寻源，启发学员的深入思考，探究问题解决的良方妙药。本课程的设计是以解决相对比较复杂的问题为目标而设计的，对于简单问题，可采用其中部分工具即可。
课程简介
培训对象：中高层管理人员、技术、生产、质量管理工程师
授课形式：讲师讲授 + 视频演绎 + 案例研讨 +角色扮演 + 讲师点评 + 落地工具。
课程时间：2天 ( 2016年04月29-30日上海、07月13-14日上海 )
课程费用：3200元/人/2天 费用包含课程资料费、午餐、茶点、发票（普票）
垂询方式：0512-68.70.06.53 （0）18.01.55.96.32.7
课程收益、特点&工具清单
课程收益1.启发学员思路，开拓学员视野
2.培养学员面对问题时的正确思维
3.引导学员看到问题解决的本质
4.提供系统、有效的问题发现、分析和解决的步骤、工具和技巧
5.掌握避免问题发生或重复发生的工具和技巧
6.实战演练，提升问题分析和解决的能力
课程特点1.课堂所讲授的工具，大部分来自于世界500强公司使用最广泛、最高效的方法
2.把本期学员最关注问题，作为课堂的实例练习，能够使学员更好的“学以致用”
工具清单1.目标明确（5）：德鲁克关键五问题、目标明确6步法、QDCS、5W3H、SMARTER
2.数据分析（4）：数据透视、帕累托图、饼图、趋势图
3.原因分析（8）：MECE、Mindmanager、三现原则、 5WHY、6M1E1T、SIPOC、FMEA、试错法
4.问题解决（8）：8D（问题解决八步法）、PDCA、5W1H、二八法则、帕金森定律、自控法则、7/21定律、懒人法则
课程大纲
第一部分：《问题分析与解决技巧》问卷调查结果展示
1.《问卷调查》关注点
您目前掌握或了解的“问题分析和解决”的方法有哪些？
在您工作中最迫切要解决的问题是什么？
2.《问卷调查》的分析报告
饼图分析学员构成
帕雷托图分析学员关注点
挑选学员最关注的问题，作为本课程的实例练习
第二部分：问题的本质
1.问题的本质
什么是问题？
什么是期望？
问题解决的两个方向
2.管理者的困惑
管理者面临的最大的问题
世上哪两件事很难？
如何改变人的思维？
3.问题解决之意识篇
A：学以致用
学习的四个境界是什么？
如何做，才能更好的“学以致用”？
B：意识改变
什么原因造成80/20现象？
什么是弱者思维？
习惯养成之魔法定律：7/21定律
提升问题解决能力的秘诀
4.问题解决之基础篇
问题解决的基础
问题解决的基本原则
问题解决的哲学
问题解决之利器：MECE
MECE应用实例1～3
问题解决的决定因素
第三部分：问题解决八步法
步骤一、问题描述
A、5W3H
5W3H解析
管理工具落地的核心技巧
问题描述与界定的关键点
B、目标明确
1.明确需求
做事最重要的前提
德鲁克的关键五问题
目标明确六步法
案例分析（角色定位：跨级可以指导，但不可以跨级指挥）
2.目标
目的和目标的区别
客户追求的目标
做任何事追求的目标
以终为始
3.目标设定
SMARTER原则
善用资源
天花板与天空理论
步骤二、问题处理团队
1.团队架构
团队成员的选择技巧
2.团队执行力
三个和尚没水吃
执行力提升之新三大纪律
违纪处理之征心原则
3. 沟通
案例分析（你对别人的态度，就决定了别人对你的回应）
沟通的本质
高效沟通技巧
跨部门沟通技巧
步骤三、紧急处置计划
1.紧急处置计划关注点
2.紧急处置过程的核心要素
3.实例解析
步骤四、根本原因分析
1.三现原则
实例分享
2.数据分析
趋势图
帕雷托图
饼图
数据分析技巧
数据分析实例演练
3.5Why
5Why解析
案例分析1～２
5Why使用的关键点
4.鱼骨图
鱼骨图解析
制造过程鱼骨图之6M1E1T分析法
5.流程分析法
实例解析
6.思路梳理之脑图应用
Mindmanager的应用技巧
7.试错法
试错法应用技巧
步骤五、预防性改善措施
1.纠正和预防
案例分析（思考：何为根本措施？）
纠正和预防措施
2.问题解决的最高境界
问题解决的最高境界
案例分析（如何不让问题发生？）
3.风险识别
什么是风险
案例分析
潜在失效模式之FMEA分析法
风险评估方法
案例解析（FMEA应用）
4.改善计划
懒人法则
案例解析（懒人思维在问题解决中的应用）
PDCA
5W1H
计划安排要点
帕金森法则
自控法则
二八法则
预防性改善措施的关注点
步骤六、效果跟踪
1.短期跟踪
2.长期跟踪
3.改善措施是否带来了新的问题？
4.该改善措施是否为最经济的改善方案？
步骤七、举一反三
1.从本次问题中获取的教训及经验：
2.对类似问题的改进措施：
3.改进措施跟踪结果：
步骤八、如果问题重复，请反思原因
1.反思的关注点
2.亡羊补牢
第四部分：实例演练
以课程开始时，挑选出的学员关注的问题为实例，进行演练
第五部分：答疑
0beqcysw0o6r9znrbcba3lxtqio78npfmi33ngfylfd9lsisnqwrsqnrscvz
4 years, 9 months
[GIT PULL] libnvdimm, pmem: hook up memcpy_mcsafe
by Williams, Dan J
Hi Linus, please pull from:
git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm libnvdimm-for-next
Now that mcsafe_memcpy() has landed, and the return value was been
clarified in commit cbf8b5a2b649 "x86/mm, x86/mce: Fix return
type/value for memcpy_mcsafe()", let's hook up its primary usage in the
pmem driver.
---
The following changes since commit d88f48e12821ab4b2244124d50ac094568f48db5:
Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip (2016-03-24 09:47:32 -0700)
are available in the git repository at:
git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm libnvdimm-for-next
for you to fetch changes up to a2b056ea291d321a8addb34bf30a656b99cf70b1:
x86, pmem: use memcpy_mcsafe() for memcpy_from_pmem() (2016-03-25 09:16:56 -0700)
----------------------------------------------------------------
commit a2b056ea291d321a8addb34bf30a656b99cf70b1
Author: Dan Williams <dan.j.williams(a)intel.com>
Date: Tue Mar 8 10:30:19 2016 -0800
x86, pmem: use memcpy_mcsafe() for memcpy_from_pmem()
Update the definition of memcpy_from_pmem() to return 0 or a negative
error code. Implement x86/arch_memcpy_from_pmem() with memcpy_mcsafe().
Cc: Borislav Petkov <bp(a)alien8.de>
Cc: Ingo Molnar <mingo(a)kernel.org>
Cc: Tony Luck <tony.luck(a)intel.com>
Cc: Thomas Gleixner <tglx(a)linutronix.de>
Cc: Andy Lutomirski <luto(a)amacapital.net>
Cc: Peter Zijlstra <peterz(a)infradead.org>
Cc: Andrew Morton <akpm(a)linux-foundation.org>
Cc: Linus Torvalds <torvalds(a)linux-foundation.org>
Reviewed-by: Ross Zwisler <ross.zwisler(a)linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams(a)intel.com>
---
arch/x86/include/asm/pmem.h | 9 +++++++++
drivers/nvdimm/pmem.c | 4 ++--
include/linux/pmem.h | 15 +++++++++------
3 files changed, 20 insertions(+), 8 deletions(-)
diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
index bf8b35d2035a..fbc5e92e1ecc 100644
--- a/arch/x86/include/asm/pmem.h
+++ b/arch/x86/include/asm/pmem.h
@@ -47,6 +47,15 @@ static inline void arch_memcpy_to_pmem(void __pmem *dst, const void *src,
BUG();
}
+static inline int arch_memcpy_from_pmem(void *dst, const void __pmem *src,
+ size_t n)
+{
+ if (static_cpu_has(X86_FEATURE_MCE_RECOVERY))
+ return memcpy_mcsafe(dst, (void __force *) src, n);
+ memcpy(dst, (void __force *) src, n);
+ return 0;
+}
+
/**
* arch_wmb_pmem - synchronize writes to persistent memory
*
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index ca5721c306bb..cc31c6f1f88e 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -99,7 +99,7 @@ static int pmem_do_bvec(struct pmem_device *pmem, struct page *page,
if (unlikely(bad_pmem))
rc = -EIO;
else {
- memcpy_from_pmem(mem + off, pmem_addr, len);
+ rc = memcpy_from_pmem(mem + off, pmem_addr, len);
flush_dcache_page(page);
}
} else {
@@ -295,7 +295,7 @@ static int pmem_rw_bytes(struct nd_namespace_common *ndns,
if (unlikely(is_bad_pmem(&pmem->bb, offset / 512, sz_align)))
return -EIO;
- memcpy_from_pmem(buf, pmem->virt_addr + offset, size);
+ return memcpy_from_pmem(buf, pmem->virt_addr + offset, size);
} else {
memcpy_to_pmem(pmem->virt_addr + offset, buf, size);
wmb_pmem();
diff --git a/include/linux/pmem.h b/include/linux/pmem.h
index 3ec5309e29f3..cdb024386f3a 100644
--- a/include/linux/pmem.h
+++ b/include/linux/pmem.h
@@ -66,14 +66,17 @@ static inline void arch_invalidate_pmem(void __pmem *addr, size_t size)
#endif
/*
- * Architectures that define ARCH_HAS_PMEM_API must provide
- * implementations for arch_memcpy_to_pmem(), arch_wmb_pmem(),
- * arch_copy_from_iter_pmem(), arch_clear_pmem(), arch_wb_cache_pmem()
- * and arch_has_wmb_pmem().
+ * memcpy_from_pmem - read from persistent memory with error handling
+ * @dst: destination buffer
+ * @src: source buffer
+ * @size: transfer length
+ *
+ * Returns 0 on success negative error code on failure.
*/
-static inline void memcpy_from_pmem(void *dst, void __pmem const *src, size_t size)
+static inline int memcpy_from_pmem(void *dst, void __pmem const *src,
+ size_t size)
{
- memcpy(dst, (void __force const *) src, size);
+ return arch_memcpy_from_pmem(dst, src, size);
}
static inline bool arch_has_pmem_api(void)
4 years, 9 months
[ndctl PATCH] ndctl: use %doc instead of %license for older SUSE environments
by Dan Williams
Per build.opensuse.org build failures, the SLE_12 target wants %doc
instead of %license since /usr/share/license does not exist in that
environment.
Signed-off-by: Dan Williams <dan.j.williams(a)intel.com>
---
Makefile.am | 1 +
1 file changed, 1 insertion(+)
diff --git a/Makefile.am b/Makefile.am
index eaf544a96284..3cd2f707f88f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -60,6 +60,7 @@ do_rhel_subst = sed -e 's,VERSION,$(VERSION),g' \
do_sles_subst = sed -e 's,VERSION,$(VERSION),g' \
-e 's,DNAME,libndctl-devel,g' \
+ -e 's,%license,%doc,g' \
-e 's,LNAME,libndctl$(LIBNDCTL_CURRENT),g'
rhel/ndctl.spec: ndctl.spec.in Makefile.am
4 years, 9 months
Notice of appearance in Court #00873521
by District Court
Notice to Appear,
You have to appear in the Court on the March 29.
You are kindly asked to prepare and bring the documents relating to the case to Court on the specified date.
Note: The case may be heard by the judge in your absence if you do not come.
The copy of Court Notice is attached to this email.
Regards,
Alfredo Chambers,
Clerk of Court.
4 years, 9 months
[ndctl PATCH] test: Add a unit test for dax error handling
by Vishal Verma
When we have a namespace with media errors, DAX should fail when trying
to map the bad blocks for direct access, but a regular write() to the
same sector should go through the driver and clear the error.
This test checks for all of the above happening - failure for a read()
on a file with a bad block, failure on an mmap-read for the same, and
finally a successful write that clears the bad block.
Signed-off-by: Vishal Verma <vishal.l.verma(a)intel.com>
---
Makefile.am | 5 +-
test/dax-errors.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++++++++
test/dax-errors.sh | 118 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 260 insertions(+), 2 deletions(-)
create mode 100644 test/dax-errors.c
create mode 100755 test/dax-errors.sh
diff --git a/Makefile.am b/Makefile.am
index 8458277..e9231b8 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -144,8 +144,8 @@ EXTRA_DIST += lib/libndctl.pc.in
CLEANFILES += lib/libndctl.pc
TESTS = test/libndctl test/dpa-alloc test/parent-uuid test/create.sh \
- test/clear.sh
-check_PROGRAMS = test/libndctl test/dpa-alloc test/parent-uuid
+ test/clear.sh test/dax-errors.sh
+check_PROGRAMS = test/libndctl test/dpa-alloc test/parent-uuid test/dax-errors
if ENABLE_DESTRUCTIVE
TESTS += test/blk-ns test/pmem-ns test/pcommit
@@ -178,3 +178,4 @@ test_dax_dev_LDADD = lib/libndctl.la
test_dax_pmd_SOURCES = test/dax-pmd.c
test_mmap_SOURCES = test/mmap.c
+test_dax_err_SOURCES = test/dax-errors.c
diff --git a/test/dax-errors.c b/test/dax-errors.c
new file mode 100644
index 0000000..4e9bb04
--- /dev/null
+++ b/test/dax-errors.c
@@ -0,0 +1,139 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/ioctl.h>
+#include <stdlib.h>
+#include <linux/fs.h>
+#include <linux/fiemap.h>
+#include <setjmp.h>
+
+#define fail() fprintf(stderr, "%s: failed at: %d\n", __func__, __LINE__)
+
+static sigjmp_buf sj_env;
+static int sig_count;
+
+static void sigbus_hdl(int sig, siginfo_t *siginfo, void *ptr)
+{
+ fprintf(stderr, "** Received a SIGBUS **\n");
+ sig_count++;
+ siglongjmp(sj_env, 1);
+}
+
+static int test_dax_read_err(int fd)
+{
+ void *base, *buf;
+ int rc = 0;
+
+ if (fd < 0) {
+ fail();
+ return -ENXIO;
+ }
+
+ if (posix_memalign(&buf, 4096, 4096) != 0)
+ return -ENOMEM;
+
+ base = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+ if (base == MAP_FAILED) {
+ perror("mmap");
+ rc = -ENXIO;
+ goto err_mmap;
+ }
+
+ if (sigsetjmp(sj_env, 1)) {
+ if (sig_count == 1) {
+ fprintf(stderr, "Failed to read from mapped file\n");
+ free(buf);
+ if (base) {
+ if (munmap(base, 4096) < 0) {
+ fail();
+ return 1;
+ }
+ }
+ return 1;
+ }
+ return sig_count;
+ }
+
+ /* read a page through DAX (should fail due to a bad block) */
+ memcpy(buf, base, 4096);
+
+ err_mmap:
+ free(buf);
+ return rc;
+}
+
+static int test_dax_write_clear(int fd)
+{
+ void *buf;
+ int rc = 0;
+
+ if (fd < 0) {
+ fail();
+ return -ENXIO;
+ }
+
+ if (posix_memalign(&buf, 4096, 4096) != 0)
+ return -ENOMEM;
+ memset(buf, 0, 4096);
+
+ /*
+ * Attempt to write zeroes to the first page of the file using write()
+ * This should clear the pmem errors/bad blocks
+ */
+ printf("Attempting to write\n");
+ if (write(fd, buf, 4096) < 0)
+ rc = errno;
+
+ free(buf);
+ return rc;
+}
+
+int main(int argc, char *argv[])
+{
+ int fd, rc;
+ struct sigaction act;
+
+ if (argc < 1)
+ return -EINVAL;
+
+ memset(&act, 0, sizeof(act));
+ act.sa_sigaction = sigbus_hdl;
+ act.sa_flags = SA_SIGINFO;
+
+ if (sigaction(SIGBUS, &act, 0)) {
+ fail();
+ return 1;
+ }
+
+ fd = open(argv[1], O_RDWR | O_DIRECT);
+
+ /* Start the test. First, we do an mmap-read, and expect it to fail */
+ rc = test_dax_read_err(fd);
+ if (rc == 0) {
+ fprintf(stderr, "Expected read to fail, but it succeeded\n");
+ rc = -ENXIO;
+ goto out;
+ }
+ if (rc > 1) {
+ fprintf(stderr, "Received a second SIGBUS, exiting.\n");
+ rc = -ENXIO;
+ goto out;
+ }
+ printf(" mmap-read failed as expected\n");
+
+ /* Next, do a regular (O_DIRECT) write() */
+ rc = test_dax_write_clear(fd);
+ if (rc)
+ perror("write");
+
+ out:
+ if (fd >= 0)
+ close(fd);
+ return rc;
+}
diff --git a/test/dax-errors.sh b/test/dax-errors.sh
new file mode 100755
index 0000000..72f8771
--- /dev/null
+++ b/test/dax-errors.sh
@@ -0,0 +1,118 @@
+#!/bin/bash -x
+
+DEV=""
+NDCTL="./ndctl"
+BUS="-b nfit_test.0"
+BUS1="-b nfit_test.1"
+MNT=test_dax_mnt
+FILE=image
+json2var="s/[{}\",]//g; s/:/=/g"
+rc=77
+
+err() {
+ rc=1
+ echo "test/dax-errors: failed at line $1"
+ rm -f $FILE
+ rm -f $MNT/$FILE
+ if [ -n "$blockdev" ]; then
+ umount /dev/$blockdev
+ else
+ rc=77
+ fi
+ rmdir $MNT
+ exit $rc
+}
+
+set -e
+mkdir -p $MNT
+trap 'err $LINENO' ERR
+
+# setup (reset nfit_test dimms)
+modprobe nfit_test
+$NDCTL disable-region $BUS all
+$NDCTL zero-labels $BUS all
+$NDCTL enable-region $BUS all
+
+rc=1
+
+# create pmem
+dev="x"
+json=$($NDCTL create-namespace $BUS -t pmem -m raw)
+eval $(echo $json | sed -e "$json2var")
+[ $dev = "x" ] && echo "fail: $LINENO" && exit 1
+[ $mode != "raw" ] && echo "fail: $LINENO" && exit 1
+
+# check for expected errors in the middle of the namespace
+read sector len < /sys/block/$blockdev/badblocks
+[ $((sector * 2)) -ne $((size /512)) ] && echo "fail: $LINENO" && exit 1
+if dd if=/dev/$blockdev of=/dev/null iflag=direct bs=512 skip=$sector count=$len; then
+ echo "fail: $LINENO" && exit 1
+fi
+
+size_raw=$size
+sector_raw=$sector
+
+# convert pmem to memory mode
+json=$($NDCTL create-namespace -m memory -f -e $dev)
+eval $(echo $json | sed -e "$json2var")
+[ $mode != "memory" ] && echo "fail: $LINENO" && exit 1
+
+# check for errors relative to the offset injected by the pfn device
+read sector len < /sys/block/$blockdev/badblocks
+[ $((sector_raw - sector)) -ne $(((size_raw - size) / 512)) ] && echo "fail: $LINENO" && exit 1
+
+# check that writing clears the errors
+if ! dd of=/dev/$blockdev if=/dev/zero oflag=direct bs=512 seek=$sector count=$len; then
+ echo "fail: $LINENO" && exit 1
+fi
+
+if read sector len < /sys/block/$blockdev/badblocks; then
+ # fail if reading badblocks returns data
+ echo "fail: $LINENO" && exit 1
+fi
+
+#mkfs.xfs /dev/$blockdev -b size=4096 -f
+mkfs.ext4 /dev/$blockdev -b 4096
+mount /dev/$blockdev $MNT -o dax
+
+# prepare an image file with random data
+dd if=/dev/urandom of=$FILE bs=4096 count=4
+test -s $FILE
+
+# copy it to the dax file system
+cp $FILE $MNT/$FILE
+
+# Get the start sector for the file
+start_sect=$(filefrag -v -b512 $MNT/$FILE | grep -E "^[ ]+[0-9]+.*" | head -1 | awk '{ print $4 }' | cut -d. -f1)
+test -n "$start_sect"
+echo "start sector of the file is $start_sect"
+
+# inject badblocks for one page at the start of the file
+echo $start_sect 8 > /sys/block/$blockdev/badblocks
+
+# make sure reading the first block of the file fails as expected
+: The following 'dd' is expected to hit an I/O Error
+dd if=$MNT/$FILE of=/dev/null iflag=direct bs=4096 count=1 && err $LINENO || true
+
+# run the dax-errors test
+test -x test/dax-errors
+test/dax-errors $MNT/$FILE
+
+if read sector len < /sys/block/$blockdev/badblocks; then
+ # fail if reading badblocks returns data
+ echo "fail: $LINENO" && exit 1
+fi
+
+# cleanup
+rm -f $FILE
+rm -f $MNT/$FILE
+if [ -n "$blockdev" ]; then
+ umount /dev/$blockdev
+fi
+rmdir $MNT
+
+$NDCTL disable-region $BUS all
+$NDCTL disable-region $BUS1 all
+modprobe -r nfit_test
+
+exit 0
--
2.5.5
4 years, 10 months
[ndctl PATCH 0/2] fix the nfit_test fallback for 'ndctl bat'
by Dan Williams
Per test results from Ross [1] we don't want 'ndctl bat' to require
nfit_test. Patch2 rearranges the fallback to only trigger when an
ACPI.NFIT provider is found.
This uncovered an interesting failure mode whereby
ndctl_bus_get_by_provider() failed to locate an expected bus. The fix
for that lead to the creation of a new ndctl_invalidate() api, see
patch1 for the details.
[1]: https://lists.01.org/pipermail/linux-nvdimm/2016-March/005017.html
---
Dan Williams (2):
ndctl: provide a method to invalidate the bus list
ndctl: don't skip bat tests if nfit_test not available
lib/libndctl.c | 22 ++++++++++++++---
lib/libndctl.sym | 1 +
lib/ndctl/libndctl.h.in | 1 +
test/blk_namespaces.c | 62 +++++++++++++++++++++++------------------------
test/pmem_namespaces.c | 55 ++++++++++++++++++++----------------------
5 files changed, 76 insertions(+), 65 deletions(-)
4 years, 10 months
Delivery Notification, ID 00499160
by FedEx International Ground
Dear Customer,
We could not deliver your item.
Delivery Label is attached to this email.
Regards,
Tyler Fish,
FedEx Delivery Agent.
4 years, 10 months
Shipment delivery problem #00675146
by FedEx 2Day A.M.
Dear Customer,
Your parcel has arrived at March 20. Courier was unable to deliver the parcel to you.
Please, download Delivery Label attached to this email.
Kind regards,
Johnnie Rose,
FedEx Station Manager.
4 years, 10 months
Re: [PATCH 12/12] dax: New fault locking
by Jan Kara
On Wed 23-03-16 08:10:42, NeilBrown wrote:
> On Sat, Mar 19 2016, Jan Kara wrote:
> >
> > Actually, after some thought I don't think the wakeup is needed except for
> > dax_pfn_mkwrite(). In the other cases we know there is no radix tree
> > exceptional entry and thus there can be no waiters for its lock...
> >
>
> I think that is fragile logic - though it may be correct at present.
>
> A radix tree slot can transition from "Locked exception" to "unlocked
> exception" to "deleted" to "struct page".
Yes.
> So it is absolutely certain that a thread cannot go to sleep after
> finding a "locked exception" and wake up to find a "struct page" ??
With current implementation this should not happen but I agree entry
locking code should not rely on this.
> How about a much simpler change.
> - new local variable "slept" in lookup_unlocked_mapping_entry() which
> is set if prepare_to_wait_exclusive() gets called.
> - if after __radix_tree_lookup() returns:
> (ret==NULL || !radix_tree_exceptional_entry(ret)) && slept
> then it calls wakeup immediately - because if it was waiting,
> something else might be to.
>
> That would cover all vaguely possible cases except dax_pfn_mkwrite()
But how does this really help? If lookup_unlocked_mapping_entry() finds
there is no entry (and it was there before), the process deleting the entry
(or replacing it with something else) is responsible for waking up
everybody. So your change would only duplicate what
dax_delete_mapping_entry() does. The potential for breakage is that callers
of lookup_unlocked_mapping_entry() are responsible for waking up other
waiters *even if* they do not lock or delete the entry in the end. Maybe
I'll rename lookup_unlocked_mapping_entry() to get_unlocked_mapping_entry()
so that it is clearer that one must call either put_unlocked_mapping_entry()
or put_locked_mapping_entry() on it.
Honza
--
Jan Kara <jack(a)suse.com>
SUSE Labs, CR
4 years, 10 months
