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path: root/networking/udhcp/signalpipe.c
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2018-03-10udhcpd: fix "not dying on SIGTERM"Denys Vlasenko
Fixes: commit 52a515d18724bbb34e3ccbbb0218efcc4eccc0a8 "udhcp: use poll() instead of select()" Feb 16 2017 udhcp_sp_read() is meant to check whether signal pipe indeed has some data to read. In the above commit, it was changed as follows: - if (!FD_ISSET(signal_pipe.rd, rfds)) + if (!pfds[0].revents) return 0; The problem is, the check was working for select() purely by accident. Caught signal interrupts select()/poll() syscalls, they return with EINTR (regardless of SA_RESTART flag in sigaction). _Then_ signal handler is invoked. IOW: they can't see any changes to fd state caused by signal haldler (in our case, signal handler makes signal pipe ready to be read). For select(), it means that rfds[] bit array is unmodified, bit of signal pipe's read fd is still set, and the above check "works": it thinks select() says there is data to read. This accident does not work for poll(): .revents stays clear, and we do not try reading signal pipe as we should. In udhcpd, we fall through and block in socket read. Further SIGTERM signals simply cause socket read to be interrupted and then restarted (since SIGTERM handler has SA_RESTART=1). Fixing this as follows: remove the check altogether. Set signal pipe read fd to nonblocking mode. Always read it in udhcp_sp_read(). If read fails, assume it's EAGAIN and return 0 ("no signal seen"). udhcpd avoids reading signal pipe on every recvd packet by looping if EINTR (using safe_poll()) - thus ensuring we have correct .revents for all fds - and calling udhcp_sp_read() only if pfds[0].revents!=0. udhcpc performs much fewer reads (typically it sleeps >99.999% of the time), there is no need to optimize it: can call udhcp_sp_read() after each poll unconditionally. To robustify socket reads, unconditionally set pfds[1].revents=0 in udhcp_sp_fd_set() (which is before poll), and check it before reading network socket in udhcpd. TODO: This might still fail: if pfds[1].revents=POLLIN, socket read may still block. There are rare cases when select/poll indicates that data can be read, but then actual read still blocks (one such case is UDP packets with wrong checksum). General advise is, if you use a poll/select loop, keep all your fds nonblocking. Maybe we should also do that to our network sockets? function old new delta udhcp_sp_setup 55 65 +10 udhcp_sp_fd_set 54 60 +6 udhcp_sp_read 46 36 -10 udhcpd_main 1451 1437 -14 udhcpc_main 2723 2708 -15 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 2/3 up/down: 16/-39) Total: -23 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-02-16udhcp: use poll() instead of select()Denys Vlasenko
function old new delta udhcp_sp_read 65 46 -19 udhcp_sp_fd_set 79 54 -25 udhcpd_main 1530 1482 -48 udhcpc_main 2780 2730 -50 ------------------------------------------------------------------------------ (add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-142) Total: -142 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-02-16udhcp: do not clobber errno by signal handlerDenys Vlasenko
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2010-03-26udhcp: cosmetic cleanups; one case of s/full_read/xread/Denys Vlasenko
function old new delta dumpleases_main 632 623 -9 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2009-11-13*: use "can't" instead of "cannot"Denys Vlasenko
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2008-09-26dhcp: add FAST_FUNC as appropriate. -160 bytes.Denis Vlasenko
2008-02-16libbb: introduce bb_signals and bb_signals_recursive,Denis Vlasenko
which sets same handler for many signals. sig_catch is nuked (bb_signals_recursive is more descriptive name). *: use them as appropriate. function old new delta bb_signals_recursive - 95 +95 bb_signals - 52 +52 run_command 258 273 +15 svlogd_main 1368 1377 +9 runsv_main 1746 1752 +6 runsvdir_main 1643 1646 +3 UNSPEC_print 64 66 +2 time_main 1128 1127 -1 ... resize_main 246 210 -36 sig_catch 63 - -63 set_fatal_sighandler 85 14 -71 ------------------------------------------------------------------------------ (add/remove: 2/1 grow/shrink: 5/24 up/down: 182/-548) Total: -366 bytes
2008-02-16*: more readable handling of pipe fds. No code changes.Denis Vlasenko
2007-11-22udhcpc: an option to perform ARP check (Jonas Danielsson ↵Denis Vlasenko
<jonas.danielsson@axis.com>) configurable, ~+300 bytes when on.
2007-09-30introduce and use close_on_exec_on(fd). -50 bytes.Denis Vlasenko
2007-05-26xpipe: introduce (saves ~170 bytes)Denis Vlasenko
udhcp/signalpipe.c: use pipe instead of socketpair.
2007-05-24udhcp: socketpair can fail if AF_UNIX is not available (e.g. if module is ↵Denis Vlasenko
not loaded). Error out on that.
2006-11-18udhcp: fix indentation and style.Denis Vlasenko
Eliminate (group) a lot of smallish *.h files Remove lots of unneeded #includes
2006-10-14add open_read_close() and similar stuffDenis Vlasenko
2006-09-06Implement optional syslog logging using ordinaryDenis Vlasenko
bb_xx_msg calls, and convert networking/* to it. The rest of bbox will be converted gradually.
2006-07-02Standardize on the vi editing directives being on the first line."Robert P. J. Day"
2006-05-08add back in udhcp supportMike Frysinger
2006-03-23remove in place of external linkMike Frysinger
2004-04-14Larry Doolittle writes:Eric Andersen
This is a bulk spelling fix patch against busybox-1.00-pre10. If anyone gets a corrupted copy (and cares), let me know and I will make alternate arrangements. Erik - please apply. Authors - please check that I didn't corrupt any meaning. Package importers - see if any of these changes should be passed to the upstream authors. I glossed over lots of sloppy capitalizations, missing apostrophes, mixed American/British spellings, and German-style compound words. What is "pretect redefined for test" in cmdedit.c? Good luck on the 1.00 release! - Larry
2003-12-18Finish remerging busybox udhcp and udhcp. Some cleanups as well.Russ Dill