chg: handle EOF reading data block...
chg: handle EOF reading data block
We recently discovered a case in production that chg uses 100% CPU and is
trying to read data forever:
recvfrom(4, "", 1814012019, 0, NULL, NULL) = 0
Using gdb, apparently readchannel() got wrong data. It was reading in an
infinite loop because rsize == 0 does not exit the loop, while the server
process had ended.
(gdb) bt
#0 ... in recv () at /lib64/libc.so.6
#1 ... in readchannel (...) at /usr/include/bits/socket2.h:45
#2 ... in readchannel (hgc=...) at hgclient.c:129
#3 ... in handleresponse (hgc=...) at hgclient.c:255
#4 ... in hgc_runcommand (hgc=..., args=<optimized>, argsize=<optimized>)
#5 ... in main (argc=...486922636, argv=..., envp=...) at chg.c:661
(gdb) frame 2
(gdb) p *hgc
$1 = {sockfd = 4, pid = 381152, ctx = {ch = 108 'l',
data = 0x7fb05164f010 "st):\nTraceback (most recent call last):\n"
"Traceback (most recent call last):\ne", maxdatasize = 1814065152,"
" datasize = 1814064225}, capflags = 16131}
This patch addresses the infinite loop issue by detecting continuously empty
responses and abort in that case.
Note that datasize can be translated to ['l', ' ', 'l', 'a']. Concatenate
datasize and data, it forms part of "Traceback (most recent call last):".
This may indicate a server-side channeledoutput issue. If it is a race
condition, we may want to use flock to protect the channels.
