Firefox 100% CPU Weirdness
Sometimes after a reboot, firefox launches into the wrong profile and seemingly changes the default profile. So I goto about:profiles, select the profile funnily named default which is no longer the real default, “Set profile as default” and “launch profile in new browser” or whatever it says. So it launched my default profile and with no tabs, proceeds to sit at 100% CPU usage for a few minutes. Exiting the firefox window left the process running. Killing pkill firefox and restarting presented the same issue. I then perf record $(pgrep firefox) and perf report > perf.report to get
7.80% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000dfcb1
2.73% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000c69d5
2.59% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a4a61
2.13% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a39e7
2.01% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a39d2
1.87% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a449b
1.70% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a5852
1.52% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a3aeb
1.45% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a449f
1.43% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a5875
1.42% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a44a6
1.23% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a586f
1.14% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a586b
1.10% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a39e0
1.07% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000dfcc4
1.03% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a4a85
1.00% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a39cc
0.99% BgIOThr~Pool #3 libmozsqlite3.so [.] 0x00000000000a44b7
...
And
grep libmozsqlite perf.report | awk '{sum+=$1;}END{print sum;}'
tells us 99.64% of samples were somewhere in libmozsqlite3. So I assume something weird was going on with a database and maybe it was deadlocked.
I then tried to discover what file it was using with lsof $(pgrep firefox) | grep sqlite
firefox 6972 andrew mem-r REG 253,2 32768 132316 /home/andrew/.cache/mozilla/firefox/qe5rlihv.default/suggest.sqlite-shm
firefox 6972 andrew mem-r REG 253,2 32768 147474 /home/andrew/.mozilla/firefox/qe5rlihv.default/storage-sync-v2.sqlite-shm
firefox 6972 andrew mem REG 253,0 1416120 268758 /usr/lib64/libsqlite3.so.0.8.6
firefox 6972 andrew mem REG 253,0 1336496 658181 /usr/lib64/firefox/libmozsqlite3.so
firefox 6972 andrew 17uw REG 253,2 1572864 131293 /home/andrew/.mozilla/firefox/qe5rlihv.default/cookies.sqlite
firefox 6972 andrew 47uw REG 253,2 869888 131322 /home/andrew/.mozilla/firefox/qe5rlihv.default/storage.sqlite
firefox 6972 andrew 50uw REG 253,2 196608 131303 /home/andrew/.mozilla/firefox/qe5rlihv.default/permissions.sqlite
firefox 6972 andrew 53u REG 253,2 524704 132444 /home/andrew/.mozilla/firefox/qe5rlihv.default/cookies.sqlite-wal
firefox 6972 andrew 88rw REG 253,2 36700160 131305 /home/andrew/.mozilla/firefox/qe5rlihv.default/places.sqlite
firefox 6972 andrew 90uw REG 253,2 229376 131241 /home/andrew/.mozilla/firefox/qe5rlihv.default/content-prefs.sqlite
firefox 6972 andrew 93u REG 253,2 2393848 137142 /home/andrew/.mozilla/firefox/qe5rlihv.default/places.sqlite-wal
firefox 6972 andrew 94rw REG 253,2 43876352 135062 /home/andrew/.mozilla/firefox/qe5rlihv.default/favicons.sqlite
firefox 6972 andrew 95u REG 253,2 327952 137444 /home/andrew/.mozilla/firefox/qe5rlihv.default/favicons.sqlite-wal
firefox 6972 andrew 96uw REG 253,2 688128 131474 /home/andrew/.mozilla/firefox/qe5rlihv.default/formhistory.sqlite
firefox 6972 andrew 98uw REG 253,2 36700160 131305 /home/andrew/.mozilla/firefox/qe5rlihv.default/places.sqlite
firefox 6972 andrew 99u REG 253,2 2393848 137142 /home/andrew/.mozilla/firefox/qe5rlihv.default/places.sqlite-wal
firefox 6972 andrew 100uw REG 253,2 43876352 135062 /home/andrew/.mozilla/firefox/qe5rlihv.default/favicons.sqlite
firefox 6972 andrew 101u REG 253,2 327952 137444 /home/andrew/.mozilla/firefox/qe5rlihv.default/favicons.sqlite-wal
firefox 6972 andrew 103rw REG 253,2 36700160 131305 /home/andrew/.mozilla/firefox/qe5rlihv.default/places.sqlite
firefox 6972 andrew 104u REG 253,2 2393848 137142 /home/andrew/.mozilla/firefox/qe5rlihv.default/places.sqlite-wal
firefox 6972 andrew 105rw REG 253,2 43876352 135062 /home/andrew/.mozilla/firefox/qe5rlihv.default/favicons.sqlite
firefox 6972 andrew 106u REG 253,2 327952 137444 /home/andrew/.mozilla/firefox/qe5rlihv.default/favicons.sqlite-wal
firefox 6972 andrew 109uw REG 253,2 163840 5508192 /home/andrew/.mozilla/firefox/qe5rlihv.default/storage/default/moz-extension+++4d415bf4-02ea-4210-9a68-1029f7d01b76/ls/data.sqlite
firefox 6972 andrew 115uw REG 253,2 65536 133582 /home/andrew/.mozilla/firefox/qe5rlihv.default/protections.sqlite
firefox 6972 andrew 118uw REG 253,2 262144 2499866 /home/andrew/.mozilla/firefox/qe5rlihv.default/storage/default/https+++www.google.com/ls/data.sqlite
firefox 6972 andrew 119rr REG 253,2 23166976 132221 /home/andrew/.cache/mozilla/firefox/qe5rlihv.default/suggest.sqlite
firefox 6972 andrew 124ur REG 253,2 32768 137685 /home/andrew/.mozilla/firefox/qe5rlihv.default/storage-sync-v2.sqlite
firefox 6972 andrew 125u REG 253,2 13444752 147466 /home/andrew/.mozilla/firefox/qe5rlihv.default/storage-sync-v2.sqlite-wal
firefox 6972 andrew 126ur REG 253,2 32768 147474 /home/andrew/.mozilla/firefox/qe5rlihv.default/storage-sync-v2.sqlite-shm
firefox 6972 andrew 127u REG 253,2 37153368 132284 /home/andrew/.cache/mozilla/firefox/qe5rlihv.default/suggest.sqlite-wal
firefox 6972 andrew 128ur REG 253,2 23166976 132221 /home/andrew/.cache/mozilla/firefox/qe5rlihv.default/suggest.sqlite
firefox 6972 andrew 129u REG 253,2 37153368 132284 /home/andrew/.cache/mozilla/firefox/qe5rlihv.default/suggest.sqlite-wal
firefox 6972 andrew 130ur REG 253,2 32768 132316 /home/andrew/.cache/mozilla/firefox/qe5rlihv.default/suggest.sqlite-shm
firefox 6972 andrew 133rw REG 253,2 36700160 131305 /home/andrew/.mozilla/firefox/qe5rlihv.default/places.sqlite
firefox 6972 andrew 135u REG 253,2 2393848 137142 /home/andrew/.mozilla/firefox/qe5rlihv.default/places.sqlite-wal
firefox 6972 andrew 136rw REG 253,2 43876352 135062 /home/andrew/.mozilla/firefox/qe5rlihv.default/favicons.sqlite
firefox 6972 andrew 137u REG 253,2 327952 137444 /home/andrew/.mozilla/firefox/qe5rlihv.default/favicons.sqlite-wal
which didn’t narrow things down. But amazingly, immediately after running this command, it stopped whatever CPU hogging it was doing.
I don’t have any theories on why lsof would do this but was happy it did. If it was something about a deadlock, something something accessing the info on the file caused the deadlock to be broken. Not sure.