Date: Mon, 27 Dec 2021 15:52:13 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Jan Mikkelsen <janm@transactionware.com> Cc: freebsd-hackers@freebsd.org Subject: Re: closefrom blocking, wchan urdlck Message-ID: <YcnFDUxa/m1xeaUS@kib.kiev.ua> In-Reply-To: <2B3BA665-D42A-4B5F-AD2F-ED10E64A7276@transactionware.com> References: <2B3BA665-D42A-4B5F-AD2F-ED10E64A7276@transactionware.com>
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On Mon, Dec 27, 2021 at 01:39:11PM +0100, Jan Mikkelsen wrote: > Hi, > > (On 11.2) > > I am occasionally seeing closefrom() block in a child process created by a call to pdfork(). > > When this does happen, it is very early after the process has started, while other threads are being created elsewhere in the process. I cannot reproduce it after the thread creation is complete. According to the sigaction man page, this should be async signal safe. > > Stack trace from the call to closefrom(): > > * frame #0: 0x000000080090276c libthr.so.3`_umtx_op_err at _umtx_op_err.S:37 > frame #1: 0x00000008008f6121 libthr.so.3`__thr_rwlock_rdlock(rwlock=<unavailable>, flags=<unavailable>, tsp=<unavailable>) at thr_umtx.c:307:10 > frame #2: 0x00000008008ff1ac libthr.so.3`_thr_rtld_rlock_acquire [inlined] _thr_rwlock_rdlock(rwlock=0x0000000800911600, flags=0, tsp=0x0000000000000000) at thr_umtx.h:232:10 > frame #3: 0x00000008008ff19b libthr.so.3`_thr_rtld_rlock_acquire(lock=0x0000000800911600) at thr_rtld.c:125 > frame #4: 0x000000080075332b ld-elf.so.1`rlock_acquire(lock=0x0000000800765270, lockstate=0x00007fffdfbfb8d0) at rtld_lock.c:208:2 > frame #5: 0x000000080074ba20 ld-elf.so.1`_rtld_bind(obj=0x0000000800769000, reloff=6072) at rtld.c:861:5 > frame #6: 0x0000000800747c7d ld-elf.so.1`_rtld_bind_start at rtld_start.S:121 > frame #7: 0x00000000006562d3 prog`Twio::ProcHandle::spawn(this=<unavailable>, command="/bin/echo", args=0x0000000800d7e000, descriptor_mapping=<unavailable>, descriptor_end=3) at prochandle_pdfork.cpp:308:2 And where is the closefrom() call in the demonstrated trace? What version of the system do you use? You need at least cbdec8db18b533f6d7be (on HEAD) or a5659943e37a74c96e (stable/13) for pdfork() to behave sanely. But you still not allowed to call non-async signal safe functions in the child before exec.
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