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Date:   Thu, 7 Jun 2018 22:19:06 +0900
From:   Tetsuo Handa <>
To:     Ming Lei <>, Ming Lei <>
Cc:     Jens Axboe <>,
        Bart Van Assche <>,
        Dmitry Vyukov <>,
        Linux Kernel Mailing List <>,
        linux-block <>,
        Johannes Thumshirn <>,,,
        "Martin K. Petersen" <>,
        Dan Williams <>,
        Christoph Hellwig <>,
        Oleksandr Natalenko <>,, Hannes Reinecke <>,,
        Ross Zwisler <>,
        Keith Busch <>,
        "open list:EXT4 FILE SYSTEM" <>
Subject: Re: INFO: task hung in blk_queue_enter

On 2018/06/07 12:29, Ming Lei wrote:
>> The vfs_fsync() isn't necessary in loop_update_dio() since both
>> generic_file_write_iter() and generic_file_read_iter() can handle
>> buffered io vs dio well.
>> I will send one patch to remove the vfs_sync() later.
> Hi Tetsuo,
> The issue might be fixed by removing this vfs_sync(), but I'd like to
> understand the idea behind since vfs_sync() shouldn't have caused
> any IO to this loop queue.
> I also tried to do the test via the following c syzbot, but can't reproduce
> it yet after running it for several hours.
> Could you share us how you reproduce it?

I just reported that syzbot started hitting vfs_sync() case.
I haven't succeeded reproducing vfs_sync() case in my environment.

But in general, I modify "any reproducer provided by syzbot that loops
forever" to call exit() if open() etc. failed, for continuing the loop
unlikely helps after hitting "Too many open files" error.

   res = syscall(__NR_memfd_create, 0x200002c0, 0);
   if (res != -1)
     r[1] = res;
+  else
+    exit(1);

Thus, I restart the reproducer in a loop from shell
rather than keep running for hours.

   while :; do echo -n .; ./a.out; done

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