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Changed ngx_chain_update_chains() to test tag first (ticket #2248). Without this change, aio used with HTTP/2 can result in connection hang, as observed with "aio threads; aio_write on;" and proxying (ticket #2248). The problem is that HTTP/2 updates buffers outside of the output filters (notably, marks them as sent), and then posts a write event to call output filters. If a filter does not call the next one for some reason (for example, because of an AIO operation in progress), this might result in a state when the owner of a buffer already called ngx_chain_update_chains() and can reuse the buffer, while the same buffer is still sitting in the busy chain of some other filter. In the particular case a buffer was sitting in output chain's ctx->busy, and was reused by event pipe. Output chain's ctx->busy was permanently blocked by it, and this resulted in connection hang. Fix is to change ngx_chain_update_chains() to skip buffers from other modules unconditionally, without trying to wait for these buffers to become empty.
author Maxim Dounin <mdounin@mdounin.ru>
date Sat, 30 Oct 2021 02:39:19 +0300
parents d620f497c50f
children
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# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


if [ $NGX_LIBATOMIC != YES ]; then

    have=NGX_HAVE_LIBATOMIC . auto/have
    CORE_INCS="$CORE_INCS $NGX_LIBATOMIC/src"
    LINK_DEPS="$LINK_DEPS $NGX_LIBATOMIC/src/libatomic_ops.a"
    CORE_LIBS="$CORE_LIBS $NGX_LIBATOMIC/src/libatomic_ops.a"

else

    ngx_feature="atomic_ops library"
    ngx_feature_name=NGX_HAVE_LIBATOMIC
    ngx_feature_run=yes
    ngx_feature_incs="#define AO_REQUIRE_CAS
                      #include <atomic_ops.h>"
    ngx_feature_path=
    ngx_feature_libs="-latomic_ops"
    ngx_feature_test="long  n = 0;
                      if (!AO_compare_and_swap(&n, 0, 1))
                          return 1;
                      if (AO_fetch_and_add(&n, 1) != 1)
                          return 1;
                      if (n != 2)
                          return 1;
                      AO_nop();"
    . auto/feature

    if [ $ngx_found = yes ]; then
        CORE_LIBS="$CORE_LIBS $ngx_feature_libs"
    else

cat << END

$0: error: libatomic_ops library was not found.

END
        exit 1
    fi
fi