[PATCH] Increase the amount of data tested in stdio-common/tst-fwrite-bz29459.c

[Florian Weimer]

* Adhemerval Zanella Netto:

> On 14/02/25 09:43, Tulio Magno Quites Machado Filho wrote:
>> Florian Weimer <fweimer@redhat.com> writes:
>> 
>>> Have you applied the patch?  We saw this as well.  But with the patch, 6
>>> million bytes are written, which I believe exceeds even the most
>>> generous kernel pipe buffer.
>> 
>> I decided to test this myself.
>> The test does fail very frequently when the system is under high load.
>> I was able to reproduce the issue in less than 10s when executing this
>> test in a loop.
>> 
>> After applying this patch, I left the test running in a loop on high
>> load. It's been running for 14h+ without any failures.
>> I believe this is indeed an effective fix.
>> 
>> Adhemerval, would you object to applying this patch as-is?
>> 
>
> The main problem with this test is pipe buffer configurable but the caller
> (in this case the shell), and on Linux the default size depends on the page
> size.
>
> If the idea is to force a pipe write error, I think using a buffer larger
> than the default pipe buffer would be better. Something like:

I believe Tulio's patch achieves that.  The idea is to stay close to the
reported reproducer.

I think there is still gap with SSH testing due to network buffering.
Fixing this gap could involve a custom head implementation that would
run from the test itself, after fork.

Thanks,
Florian