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fac0f645df
A crash reported in github issue #880 looks impossible unless pendconn_cond_unlink() occasionally sees a null leaf_p when attempting to remove an entry, which seems to be confirmed by the reporter. What seems to be happening is that depending on compiler optimizations, this pointer can appear as null while pointers are moved if one of the node's parents is removed from or inserted into the tree. There's no explicit null of the pointer during these operations but those pointers are rewritten in multiple steps and nothing prevents this situation from happening, and there are no particular barrier nor atomic ops around this. This test was used to avoid unnecessary locking, for already deleted entries, but looking at the code it appears that pendconn_free() already resets s->pend_pos that's used as <p> there, and that the other call reasons are after an error where the connection will be dropped as well. So we don't save anything by doing this test, and make it unsafe. The older code used to check for list emptiness there and not inside pendconn_unlink(), which explains why the code has stayed there. Let's just remove this now. Thanks to @jaroslawr for reporting this issue in great details and for testing the proposed fix. This should be backpored to 1.8, where the test on LIST_ISEMPTY should be moved to pendconn_unlink() instead (inside the lock, just like 2.0+).
115 lines
3.4 KiB
C
115 lines
3.4 KiB
C
/*
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* include/haproxy/queue.h
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* This file defines everything related to queues.
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*
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* Copyright (C) 2000-2020 Willy Tarreau - w@1wt.eu
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation, version 2.1
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* exclusively.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef _HAPROXY_QUEUE_H
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#define _HAPROXY_QUEUE_H
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#include <haproxy/api.h>
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#include <haproxy/backend.h>
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#include <haproxy/pool.h>
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#include <haproxy/proxy-t.h>
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#include <haproxy/queue-t.h>
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#include <haproxy/server-t.h>
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#include <haproxy/stream-t.h>
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extern struct pool_head *pool_head_pendconn;
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struct pendconn *pendconn_add(struct stream *strm);
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int pendconn_dequeue(struct stream *strm);
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void process_srv_queue(struct server *s);
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unsigned int srv_dynamic_maxconn(const struct server *s);
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int pendconn_redistribute(struct server *s);
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int pendconn_grab_from_px(struct server *s);
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void pendconn_unlink(struct pendconn *p);
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/* Removes the pendconn from the server/proxy queue. It supports being called
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* with NULL for pendconn and with a pendconn not in the list. It is the
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* function to be used by default when unsure. Do not call it with server
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* or proxy locks held however.
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*/
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static inline void pendconn_cond_unlink(struct pendconn *p)
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{
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if (p)
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pendconn_unlink(p);
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}
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/* Releases the pendconn associated to stream <s> if it has any, and decreases
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* the pending count if needed. The connection might have been queued to a
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* specific server as well as to the proxy. The stream also gets marked
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* unqueued.
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*
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* This function must be called by the stream itself, so in the context of
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* process_stream, without any lock held among the pendconn, the server's queue
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* nor the proxy's queue.
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*/
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static inline void pendconn_free(struct stream *s)
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{
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struct pendconn *p = s->pend_pos;
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if (p) {
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pendconn_cond_unlink(p);
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s->pend_pos = NULL;
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pool_free(pool_head_pendconn, p);
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}
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}
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/* Returns 0 if all slots are full on a server, or 1 if there are slots available. */
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static inline int server_has_room(const struct server *s) {
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return !s->maxconn || s->cur_sess < srv_dynamic_maxconn(s);
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}
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/* returns 0 if nothing has to be done for server <s> regarding queued connections,
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* and non-zero otherwise. If the server is down, we only check its own queue. Suited
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* for and if/else usage.
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*/
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static inline int may_dequeue_tasks(const struct server *s, const struct proxy *p) {
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return (s && (s->nbpend || (p->nbpend && srv_currently_usable(s))) &&
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(!s->maxconn || s->cur_sess < srv_dynamic_maxconn(s)));
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}
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static inline int queue_limit_class(int class)
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{
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if (class < -0x7ff)
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return -0x7ff;
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if (class > 0x7ff)
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return 0x7ff;
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return class;
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}
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static inline int queue_limit_offset(int offset)
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{
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if (offset < -0x7ffff)
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return -0x7ffff;
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if (offset > 0x7ffff)
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return 0x7ffff;
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return offset;
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}
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#endif /* _HAPROXY_QUEUE_H */
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/*
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* Local variables:
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* c-indent-level: 8
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* c-basic-offset: 8
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* End:
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*/
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