Re: [Bug 219094] gen_kheaders.sh gets stuck in an infinite loop (on tmpfs)

[Chuck Lever III <chuck.lever@oracle.com>]

> On Jul 25, 2024, at 9:05 PM, Hugh Dickins <hughd@google.com> wrote:
> 
> Please send responses by email reply-to-all rather than through bugzilla.
> 
> On Thu, 25 Jul 2024, bugzilla-daemon@kernel.org wrote:
> 
>> https://bugzilla.kernel.org/show_bug.cgi?id=219094
>> 
>> Hong, Yifan (jacky8hyf@gmail.com) reports:
>> 
>> I have hit a similar bug to https://bugzilla.kernel.org/show_bug.cgi?id=217681, but on tmpfs. 
>> 
>> Here's a small reproducer for the bug, from https://bugzilla.kernel.org/show_bug.cgi?id=217681#c1:
>> 
>> ```
>> #include <sys/types.h>
>> #include <dirent.h>
>> #include <stdio.h>
>> 
>> int main(int argc, char *argv[])
>> {
>>  DIR *dir = opendir(".");
>>  struct dirent *dd;
>> 
>>  while ((dd = readdir(dir))) {
>>    printf("%s\n", dd->d_name);
>>    rename(dd->d_name, "TEMPFILE");
>>    rename("TEMPFILE", dd->d_name);
>>  }
>>  closedir(dir);
>> }
>> ```
>> 
>> Run in a directory with multiple (2000) files, it does not complete on tmpfs. I created a tmpfs mount point via
>> 
>> ```
>> mount -o size=1G -t tmpfs none ~/tmpfs/mount/
>> ```
>> 
>> The other bug was fixed on btrfs via https://lore.kernel.org/linux-btrfs/c9ceb0e15d92d0634600603b38965d9b6d986b6d.1691923900.git.fdmanana@suse.com/. Could anyone please see if the issue can be ported to tmpfs as well? Thanks in advance!
>> 
>> I am using a `Linux version 6.6.15` kernel, if that's useful to anyone.
> 
> Thank you for reporting, Yifan; and thank you for the easy reproducer, Rob.
> 
> Yes, it appears that tmpfs was okay for this up to v6.5, but cannot cope
> from v6.6 onwards - a likely-sounding fix went into v6.10, but that must
> have been for something different, v6.10 still failing on this repro.
> 
> Chuck, I'm hoping that you will have time to spare to solve this in latest;
> and then we shall want a backport (of only this fix, or more?) for v6.6 LTS.

Well, I don't have time, but I will indeed have a look. ;-)
This does look awfully similar to the rename bug I fixed
recently in this code.

Meanwhile, can I ask that someone else begin collecting these
reproducers to add to fstests? Christian and I have both run
fstests repeatedly against tmpfs and it does not seem to find
these corner cases.

--
Chuck Lever