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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.
This commit is contained in:
Maxim Dounin 2021-10-30 02:39:19 +03:00
parent 19a9a22ffc
commit bede588761
1 changed files with 4 additions and 4 deletions
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8
src/core/ngx_buf.c
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@ -203,16 +203,16 @@ ngx_chain_update_chains(ngx_pool_t *p, ngx_chain_t **free, ngx_chain_t **busy,
while (*busy) {
cl = *busy;
if (ngx_buf_size(cl->buf) != 0) {
break;
}
if (cl->buf->tag != tag) {
*busy = cl->next;
ngx_free_chain(p, cl);
continue;
}
if (ngx_buf_size(cl->buf) != 0) {
break;
}
cl->buf->pos = cl->buf->start;
cl->buf->last = cl->buf->start;