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authorSzabolcs Nagy <szabolcs.nagy@arm.com>2021-02-16 12:55:13 +0000
committerSzabolcs Nagy <szabolcs.nagy@arm.com>2021-04-13 08:43:40 +0100
commitb116855de71098ef7dd2875dd3237f8f3ecc12c2 (patch)
tree6da94b9ca548a5042d743626fdbe1990fa5221a2 /signal/siggetmask.c
parentf8ea2b9982e39fd950d157f5dba31121ceb51df3 (diff)
downloadglibc-nsz/bug19329-v2.tar.gz
glibc-nsz/bug19329-v2.tar.xz
glibc-nsz/bug19329-v2.zip
RFC elf: Fix slow tls access after dlopen [BZ #19924] nsz/bug19329-v2
In short: __tls_get_addr checks the global generation counter,
_dl_update_slotinfo updates up to the generation of the accessed
module. If the global generation is newer than geneneration of the
module then __tls_get_addr keeps hitting the slow path that updates
the dtv.

Possible approaches i can see:

1. update to global generation instead of module,
2. check the module generation in the fast path.

This patch is 1.: it needs additional sync (load acquire) so the
slotinfo list is up to date with the observed global generation.

Approach 2. would require walking the slotinfo list at all times.
I don't know how to make that fast with many modules.

Note: in the x86_64 version of dl-tls.c the generation is only loaded
once, since relaxed mo is not faster than acquire mo load.

I have not benchmarked this yet.
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