From 7b9bc5d4d1c061095a2391dbe32cf4d205c031bc Mon Sep 17 00:00:00 2001 From: Maxim Dounin Date: Wed, 30 May 2018 15:40:34 +0300 Subject: Limit req: improved handling of negative times. Negative times can appear since workers only update time on an event loop iteration start. If a worker was blocked for a long time during an event loop iteration, it is possible that another worker already updated the time stored in the node. As such, time since last update of the node (ms) will be negative. Previous code used ngx_abs(ms) in the calculations. That is, negative times were effectively treated as positive ones. As a result, it was not possible to maintain high request rates, where the same node can be updated multiple times from during an event loop iteration. In particular, this affected setups with many SSL handshakes, see http://mailman.nginx.org/pipermail/nginx/2018-May/056291.html. Fix is to only update the last update time stored in the node if the new time is larger than previously stored one. If a future time is stored in the node, we preserve this time as is. To prevent breaking things on platforms without monotonic time available if system time is updated backwards, a safety limit of 60 seconds is used. If the time stored in the node is more than 60 seconds in the future, we assume that the time was changed backwards and update lr->last to the current time. --- src/http/modules/ngx_http_limit_req_module.c | 29 ++++++++++++++++++++++++---- 1 file changed, 25 insertions(+), 4 deletions(-) (limited to 'src/http/modules/ngx_http_limit_req_module.c') diff --git a/src/http/modules/ngx_http_limit_req_module.c b/src/http/modules/ngx_http_limit_req_module.c index 579b13c84..63ec2de3f 100644 --- a/src/http/modules/ngx_http_limit_req_module.c +++ b/src/http/modules/ngx_http_limit_req_module.c @@ -399,7 +399,14 @@ ngx_http_limit_req_lookup(ngx_http_limit_req_limit_t *limit, ngx_uint_t hash, ms = (ngx_msec_int_t) (now - lr->last); - excess = lr->excess - ctx->rate * ngx_abs(ms) / 1000 + 1000; + if (ms < -60000) { + ms = 1; + + } else if (ms < 0) { + ms = 0; + } + + excess = lr->excess - ctx->rate * ms / 1000 + 1000; if (excess < 0) { excess = 0; @@ -413,7 +420,11 @@ ngx_http_limit_req_lookup(ngx_http_limit_req_limit_t *limit, ngx_uint_t hash, if (account) { lr->excess = excess; - lr->last = now; + + if (ms) { + lr->last = now; + } + return NGX_OK; } @@ -509,13 +520,23 @@ ngx_http_limit_req_account(ngx_http_limit_req_limit_t *limits, ngx_uint_t n, now = ngx_current_msec; ms = (ngx_msec_int_t) (now - lr->last); - excess = lr->excess - ctx->rate * ngx_abs(ms) / 1000 + 1000; + if (ms < -60000) { + ms = 1; + + } else if (ms < 0) { + ms = 0; + } + + excess = lr->excess - ctx->rate * ms / 1000 + 1000; if (excess < 0) { excess = 0; } - lr->last = now; + if (ms) { + lr->last = now; + } + lr->excess = excess; lr->count--; -- cgit