Messages in this thread | | | Date | Tue, 1 Aug 2017 21:09:07 +0800 | From | Lu Fengqi <> | Subject | Re: [PATCH -mm] fault-inject: avoid unwanted data race to task->fail_nth |
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On Fri, Jul 14, 2017 at 01:14:52AM +0900, Akinobu Mita wrote: >The fault-inject-make-fail-nth-read-write-interface-symmetric.patch in >-mm tree allows users to set task->fail_nth for non current task by procfs. >On the other hand, the current task's fail_nth is decreased to zero in >fault-injection path without any specific locks. > >So we need to prevent the task->fail_nth from being unexpected value by >data races (for example, setting task->fail_nth to zero while decreasing >the current->fail_nth). In this fix, we use READ_ONCE() and WRITE_ONCE() >to prevent the compiler from creating unsolicited accesses. > >Cc: Dmitry Vyukov <dvyukov@google.com> >Reported-by: Dmitry Vyukov <dvyukov@google.com> >Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> >--- > fs/proc/base.c | 5 +++-- > lib/fault-inject.c | 7 +++++-- > 2 files changed, 8 insertions(+), 4 deletions(-) > >diff --git a/fs/proc/base.c b/fs/proc/base.c >index ecc8a25..719c2e9 100644 >--- a/fs/proc/base.c >+++ b/fs/proc/base.c >@@ -1370,7 +1370,7 @@ static ssize_t proc_fail_nth_write(struct file *file, const char __user *buf, > task = get_proc_task(file_inode(file)); > if (!task) > return -ESRCH; >- task->fail_nth = n; >+ WRITE_ONCE(task->fail_nth, n); > put_task_struct(task); > > return count; >@@ -1386,7 +1386,8 @@ static ssize_t proc_fail_nth_read(struct file *file, char __user *buf, > task = get_proc_task(file_inode(file)); > if (!task) > return -ESRCH; >- len = snprintf(numbuf, sizeof(numbuf), "%u\n", task->fail_nth); >+ len = snprintf(numbuf, sizeof(numbuf), "%u\n", >+ READ_ONCE(task->fail_nth)); > len = simple_read_from_buffer(buf, count, ppos, numbuf, len); > put_task_struct(task); > >diff --git a/lib/fault-inject.c b/lib/fault-inject.c >index 09ac73c1..7d315fd 100644 >--- a/lib/fault-inject.c >+++ b/lib/fault-inject.c >@@ -107,9 +107,12 @@ static inline bool fail_stacktrace(struct fault_attr *attr) > > bool should_fail(struct fault_attr *attr, ssize_t size) > { >- if (in_task() && current->fail_nth) { >- if (--current->fail_nth == 0) >+ if (in_task()) { >+ unsigned int fail_nth = READ_ONCE(current->fail_nth); >+ >+ if (fail_nth && !WRITE_ONCE(current->fail_nth, fail_nth - 1)) > goto fail; >+ > return false; > } > >-- >2.7.4 > > > hi
I'm a btrfs developer. I found that fail_make_request didn't produce the expected IO ERROR when running xfstests on linux 4.13-rc1.
That testcase enable fail_make_request by the following commands: # echo 100 > /sys/kernel/debug/fail_make_request/probability # echo 2 > /sys/kernel/debug/fail_make_request/times # echo 0 > /sys/kernel/debug/fail_make_request/verbose # echo 1 > /sys/block/sda/sda1/make-it-fail # dd if=/dev/zero of=/dev/sda1 bs=128K count=1 oflag=direct
As I understand it, after applying this patch, I have to write /proc/<dd pid>/file-nth firstly so that dd process can catch the IO ERROR. However, the dd process is so fast that I can't write file-nth.
So, could you tell me how to produce IO ERROR under these circumstances?
A response would be very much appreciated. Thank you for your time.
-- Thanks, Lu
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