Re: [RESEND] [PATCH] VFS: make file->f_pos access atomic on 32bit arch

[Andi Kleen]

Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> writes:

> Hi Andrew.
>
> Currently reading or writing file->f_pos is not atomic on 32bit environment,
> so two or more simultaneous access can corrupt file->f_pos value.
> There are some past discussions about this issue, but this is not fixed yet.
> http://marc.info/?l=linux-kernel&m=120764199819899&w=2
> http://marc.info/?l=linux-kernel&m=114490379102476&w=2

Have you benchmarked if cmpxchg is cheaper than the seqlock?  It's not
clear to me a seqlock is really the right locking primitive for
this. Normally seqlocks should be used when reading is much more
frequent than writing, but it's doubtful that this is actually the
case for f_pos.

-Andi

-- 
ak@xxxxxxxxxxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/