Re: [PATCH v2 06/14] elf: Use relaxed atomics for racy accesses [BZ #19329]

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 04/15/2021 15:21, Adhemerval Zanella wrote:
> On 13/04/2021 05:19, Szabolcs Nagy via Libc-alpha wrote:
> > This is a follow up patch to the fix for bug 19329.  This adds
> > relaxed MO atomics to accesses that are racy, but relaxed MO is
> > enough.
> 
> Could you extend a bit why relaxed MO should be suffice?

is it ok to change the commit message to:

This is a follow up patch to the fix for bug 19329.  This adds relaxed
MO atomics to accesses that are racy, but relaxed MO is enough.

The racy accesses all follow the pattern that the write is behind the
dlopen lock, but a read can happen concurrently (e.g. during tls access)
without holding the lock.  For slotinfo entries the read value only
matters if it reads from a synchronized write in dlopen or dlclose,
otherwise the related dtv entry is not valid to access so it is fine to
leave it in inconsistent state. Same for GL(dl_tls_max_dtv_idx) and
GL(dl_tls_generation), but there we rely on the read value being larger
than the last written value that was synchronized.

> 
> Patch looks good, just a small request below.
> 
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

thanks.