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[nginx] Fixed request termination with AIO and subrequests (ticket #2555).

Sergey Kandaurov
January 30, 2024 10:10AM
details: https://hg.nginx.org/nginx/rev/0de20f43db25
branches:
changeset: 9203:0de20f43db25
user: Maxim Dounin <mdounin@mdounin.ru>
date: Tue Jan 30 03:20:05 2024 +0300
description:
Fixed request termination with AIO and subrequests (ticket #2555).

When a request was terminated due to an error via ngx_http_terminate_request()
while an AIO operation was running in a subrequest, various issues were
observed. This happened because ngx_http_request_finalizer() was only set
in the subrequest where ngx_http_terminate_request() was called, but not
in the subrequest where the AIO operation was running. After completion
of the AIO operation normal processing of the subrequest was resumed, leading
to issues.

In particular, in case of the upstream module, termination of the request
called upstream cleanup, which closed the upstream connection. Attempts to
further work with the upstream connection after AIO operation completion
resulted in segfaults in ngx_ssl_recv(), "readv() failed (9: Bad file
descriptor) while reading upstream" errors, or socket leaks.

In ticket #2555, issues were observed with the following configuration
with cache background update (with thread writing instrumented to
introduce a delay, when a client closes the connection during an update):

location = /background-and-aio-write {
proxy_pass ...
proxy_cache one;
proxy_cache_valid 200 1s;
proxy_cache_background_update on;
proxy_cache_use_stale updating;
aio threads;
aio_write on;
limit_rate 1000;
}

Similarly, the same issue can be seen with SSI, and can be caused by
errors in subrequests, such as in the following configuration
(where "/proxy" uses AIO, and "/sleep" returns 444 after some delay,
causing request termination):

location = /ssi-active-boom {
ssi on;
ssi_types *;
return 200 '
<!--#include virtual="/proxy" -->
<!--#include virtual="/sleep" -->
';
limit_rate 1000;
}

Or the same with both AIO operation and the error in non-active subrequests
(which needs slightly different handling, see below):

location = /ssi-non-active-boom {
ssi on;
ssi_types *;
return 200 '
<!--#include virtual="/static" -->
<!--#include virtual="/proxy" -->
<!--#include virtual="/sleep" -->
';
limit_rate 1000;
}

Similarly, issues can be observed with just static files. However,
with static files potential impact is limited due to timeout safeguards
in ngx_http_writer(), and the fact that c->error is set during request
termination.

In a simple configuration with an AIO operation in the active subrequest,
such as in the following configuration, the connection is closed right
after completion of the AIO operation anyway, since ngx_http_writer()
tries to write to the connection and fails due to c->error set:

location = /ssi-active-static-boom {
ssi on;
ssi_types *;
return 200 '
<!--#include virtual="/static-aio" -->
<!--#include virtual="/sleep" -->
';
limit_rate 1000;
}

In the following configuration, with an AIO operation in a non-active
subrequest, the connection is closed only after send_timeout expires:

location = /ssi-non-active-static-boom {
ssi on;
ssi_types *;
return 200 '
<!--#include virtual="/static" -->
<!--#include virtual="/static-aio" -->
<!--#include virtual="/sleep" -->
';
limit_rate 1000;
}

Fix is to introduce r->main->terminated flag, which is to be checked
by AIO event handlers when the r->main->blocked counter is decremented.
When the flag is set, handlers are expected to wake up the connection
instead of the subrequest (which might be already cleaned up).

Additionally, now ngx_http_request_finalizer() is always set in the
active subrequest, so waking up the connection properly finalizes the
request even if termination happened in a non-active subrequest.

diffstat:

src/http/ngx_http_copy_filter_module.c | 19 ++++++--
src/http/ngx_http_file_cache.c | 69 +++++++++++++++++++++++++--------
src/http/ngx_http_request.c | 5 ++
src/http/ngx_http_request.h | 1 +
src/http/ngx_http_upstream.c | 6 +-
5 files changed, 74 insertions(+), 26 deletions(-)

diffs (218 lines):

diff -r e88cdaa0f1ff -r 0de20f43db25 src/http/ngx_http_copy_filter_module.c
--- a/src/http/ngx_http_copy_filter_module.c Mon Jan 29 10:31:37 2024 +0300
+++ b/src/http/ngx_http_copy_filter_module.c Tue Jan 30 03:20:05 2024 +0300
@@ -208,9 +208,18 @@ ngx_http_copy_aio_event_handler(ngx_even
r->main->blocked--;
r->aio = 0;

- r->write_event_handler(r);
+ if (r->main->terminated) {
+ /*
+ * trigger connection event handler if the request was
+ * terminated
+ */

- ngx_http_run_posted_requests(c);
+ c->write->handler(c->write);
+
+ } else {
+ r->write_event_handler(r);
+ ngx_http_run_posted_requests(c);
+ }
}

#endif
@@ -331,11 +340,11 @@ ngx_http_copy_thread_event_handler(ngx_e

#endif

- if (r->done) {
+ if (r->done || r->main->terminated) {
/*
* trigger connection event handler if the subrequest was
- * already finalized; this can happen if the handler is used
- * for sendfile() in threads
+ * already finalized (this can happen if the handler is used
+ * for sendfile() in threads), or if the request was terminated
*/

c->write->handler(c->write);
diff -r e88cdaa0f1ff -r 0de20f43db25 src/http/ngx_http_file_cache.c
--- a/src/http/ngx_http_file_cache.c Mon Jan 29 10:31:37 2024 +0300
+++ b/src/http/ngx_http_file_cache.c Tue Jan 30 03:20:05 2024 +0300
@@ -14,7 +14,7 @@
static ngx_int_t ngx_http_file_cache_lock(ngx_http_request_t *r,
ngx_http_cache_t *c);
static void ngx_http_file_cache_lock_wait_handler(ngx_event_t *ev);
-static void ngx_http_file_cache_lock_wait(ngx_http_request_t *r,
+static ngx_int_t ngx_http_file_cache_lock_wait(ngx_http_request_t *r,
ngx_http_cache_t *c);
static ngx_int_t ngx_http_file_cache_read(ngx_http_request_t *r,
ngx_http_cache_t *c);
@@ -463,6 +463,7 @@ ngx_http_file_cache_lock(ngx_http_reques
static void
ngx_http_file_cache_lock_wait_handler(ngx_event_t *ev)
{
+ ngx_int_t rc;
ngx_connection_t *c;
ngx_http_request_t *r;

@@ -474,13 +475,31 @@ ngx_http_file_cache_lock_wait_handler(ng
ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
"http file cache wait: \"%V?%V\"", &r->uri, &r->args);

- ngx_http_file_cache_lock_wait(r, r->cache);
-
- ngx_http_run_posted_requests(c);
+ rc = ngx_http_file_cache_lock_wait(r, r->cache);
+
+ if (rc == NGX_AGAIN) {
+ return;
+ }
+
+ r->cache->waiting = 0;
+ r->main->blocked--;
+
+ if (r->main->terminated) {
+ /*
+ * trigger connection event handler if the request was
+ * terminated
+ */
+
+ c->write->handler(c->write);
+
+ } else {
+ r->write_event_handler(r);
+ ngx_http_run_posted_requests(c);
+ }
}


-static void
+static ngx_int_t
ngx_http_file_cache_lock_wait(ngx_http_request_t *r, ngx_http_cache_t *c)
{
ngx_uint_t wait;
@@ -495,7 +514,7 @@ ngx_http_file_cache_lock_wait(ngx_http_r
ngx_log_error(NGX_LOG_INFO, r->connection->log, 0,
"cache lock timeout");
c->lock_timeout = 0;
- goto wakeup;
+ return NGX_OK;
}

cache = c->file_cache;
@@ -513,14 +532,10 @@ ngx_http_file_cache_lock_wait(ngx_http_r

if (wait) {
ngx_add_timer(&c->wait_event, (timer > 500) ? 500 : timer);
- return;
+ return NGX_AGAIN;
}

-wakeup:
-
- c->waiting = 0;
- r->main->blocked--;
- r->write_event_handler(r);
+ return NGX_OK;
}


@@ -753,9 +768,18 @@ ngx_http_cache_aio_event_handler(ngx_eve
r->main->blocked--;
r->aio = 0;

- r->write_event_handler(r);
-
- ngx_http_run_posted_requests(c);
+ if (r->main->terminated) {
+ /*
+ * trigger connection event handler if the request was
+ * terminated
+ */
+
+ c->write->handler(c->write);
+
+ } else {
+ r->write_event_handler(r);
+ ngx_http_run_posted_requests(c);
+ }
}

#endif
@@ -836,9 +860,18 @@ ngx_http_cache_thread_event_handler(ngx_
r->main->blocked--;
r->aio = 0;

- r->write_event_handler(r);
-
- ngx_http_run_posted_requests(c);
+ if (r->main->terminated) {
+ /*
+ * trigger connection event handler if the request was
+ * terminated
+ */
+
+ c->write->handler(c->write);
+
+ } else {
+ r->write_event_handler(r);
+ ngx_http_run_posted_requests(c);
+ }
}

#endif
diff -r e88cdaa0f1ff -r 0de20f43db25 src/http/ngx_http_request.c
--- a/src/http/ngx_http_request.c Mon Jan 29 10:31:37 2024 +0300
+++ b/src/http/ngx_http_request.c Tue Jan 30 03:20:05 2024 +0300
@@ -2694,6 +2694,8 @@ ngx_http_terminate_request(ngx_http_requ
ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
"http terminate request count:%d", mr->count);

+ mr->terminated = 1;
+
if (rc > 0 && (mr->headers_out.status == 0 || mr->connection->sent == 0)) {
mr->headers_out.status = rc;
}
@@ -2716,8 +2718,11 @@ ngx_http_terminate_request(ngx_http_requ
if (mr->write_event_handler) {

if (mr->blocked) {
+ r = r->connection->data;
+
r->connection->error = 1;
r->write_event_handler = ngx_http_request_finalizer;
+
return;
}

diff -r e88cdaa0f1ff -r 0de20f43db25 src/http/ngx_http_request.h
--- a/src/http/ngx_http_request.h Mon Jan 29 10:31:37 2024 +0300
+++ b/src/http/ngx_http_request.h Tue Jan 30 03:20:05 2024 +0300
@@ -550,6 +550,7 @@ struct ngx_http_request_s {
unsigned root_tested:1;
unsigned done:1;
unsigned logged:1;
+ unsigned terminated:1;

unsigned buffered:4;

diff -r e88cdaa0f1ff -r 0de20f43db25 src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c Mon Jan 29 10:31:37 2024 +0300
+++ b/src/http/ngx_http_upstream.c Tue Jan 30 03:20:05 2024 +0300
@@ -3997,11 +3997,11 @@ ngx_http_upstream_thread_event_handler(n

#endif

- if (r->done) {
+ if (r->done || r->main->terminated) {
/*
* trigger connection event handler if the subrequest was
- * already finalized; this can happen if the handler is used
- * for sendfile() in threads
+ * already finalized (this can happen if the handler is used
+ * for sendfile() in threads), or if the request was terminated
*/

c->write->handler(c->write);
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Subject Author Views Posted

[nginx] Fixed request termination with AIO and subrequests (ticket #2555).

Sergey Kandaurov 137 January 30, 2024 10:10AM



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