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A problem involving server slowstart was reported by @max2k1 in issue #197. The problem is that pendconn_grab_from_px() takes the proxy lock while already under the server's lock while process_srv_queue() first takes the proxy's lock then the server's lock. While the latter seems more natural, it is fundamentally incompatible with mayn other operations performed on servers, namely state change propagation, where the proxy is only known after the server and cannot be locked around the servers. Howwever reversing the lock in process_srv_queue() is trivial and only the few functions related to dynamic cookies need to be adjusted for this so that the proxy's lock is taken for each server operation. This is possible because the proxy's server list is built once at boot time and remains stable. So this is what this patch does. The comments in the proxy and server structs were updated to mention this rule that the server's lock may not be taken under the proxy's lock but may enclose it. Another approach could consist in using a second lock for the proxy's queue which would be different from the regular proxy's lock, but given that the operations above are rare and operate on small servers list, there is no reason for overdesigning a solution. This fix was successfully tested with 10000 servers in a backend where adjusting the dyncookies in loops over the CLI didn't have a measurable impact on the traffic. The only workaround without the fix is to disable any occurrence of "slowstart" on server lines, or to disable threads using "nbthread 1". This must be backported as far as 1.8.