GNU bug report logs

#31785 Multiple client 'build-paths' RPCs can lead to daemon deadlock

Package	Source(s)		Maintainer(s)
guix		PTS Buildd Popcon

Reported by ludo@gnu.org (Ludovic Courtès)
Date 2018-06-11T14:07:02
Severity important

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Report forwarded to bug-guix@gnu.org:
bug#31785; Package guix. (Mon, 11 Jun 2018 14:07:02 GMT) (full text, mbox, link).

Acknowledgement sent to ludo@gnu.org (Ludovic Courtès):
New bug report received and forwarded. Copy sent to bug-guix@gnu.org. (Mon, 11 Jun 2018 14:07:03 GMT) (full text, mbox, link).

Message #5 received at submit@debbugs.gnu.org (full text, mbox, reply):

Hello,

I tried running this:

  guix build --max-jobs=200 $(guix gc -R $(guix build -d inkscape --no-grafts) | sort) & \
  guix build --max-jobs=200 $(guix gc -R $(guix build -d inkscape --no-grafts) | sort -r)

… also in parallel with this (for good measure):

  guix build --max-jobs=200 $(guix gc -R $(guix build -d inkscape --no-grafts) | sort -R)

Since we have 3 clients, that leads to 3 guix-daemon processes, and
those are stuck in a deadlock:

--8<---------------cut here---------------start------------->8---
$ ps aux | grep guix-daemon
[…]
root     20501  0.6  0.0  39292 12012 ?        Ss   15:51   0:01 guix-daemon 20455
root     20503  4.3  0.0  39420 12096 ?        Ss   15:51   0:12 guix-daemon 20491
root     22154  0.0  0.0  39028 11016 ?        Ss   15:52   0:00 guix-daemon 22148
$ sudo strace -p 22154 -t
strace: Process 22154 attached
15:57:03 select(0, 0x7ffdca30b610, NULL, NULL, {tv_sec=1, tv_usec=314189}) = 0 (Timeout)
15:57:04 openat(AT_FDCWD, "/gnu/store/ghc9vcc8ydv305jz0spd73qrrf30gxik-binutils-bootstrap-0.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/5hdpffkgkfszpsin2ir50zscz06x0mb5-coreutils-8.29-debug.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/aasfcliv85frq3aawpa4rw18nvlvl735-gettext-minimal-0.19.8.1.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/j1kpzcpi1m1ihzwyqb60zd4s74yp85g8-glibc-bootstrap-0.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/4llnxsgr6mxxj6pk21d9vbwaxnkbn99k-gnutls-3.5.18-doc.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/7rs9qx86f2w4hjbf9wjm10k4m2vvlbyv-groff-1.22.3-doc.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/d645d919gp1zk8v65qa2r4ia5x1c5n6k-libstdc++-5.5.0.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/amcs7l0ynj1qg6fp9ll3asiamd4zsq75-m4-1.4.18.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/p262qk7zsd2wnlal6x1jax2xbqvdddqq-m4-1.4.18.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/zvvgr301hz95ac15rp0wsjy5j4cdgkg4-module-import-compiled.lock", O_RDWR|O_CREAT, 0600) = 8
15:57:04 fcntl(8, F_GETFD)              = 0
15:57:04 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:57:04 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:57:04 close(8)                       = 0
15:57:04 openat(AT_FDCWD, "/gnu/store/760kj698c9x1vcmlzk1qr8i9hqw961n3-openssl-1.0.2o-doc.lock", O_RDWR|O_CREAT, 0600) = 8
^C
$ sudo strace -p 20503 -t
strace: Process 20503 attached
15:58:23 select(445, [15 54 159 177 321 411 414 444], NULL, NULL, {tv_sec=1, tv_usec=595302}) = 0 (Timeout)
15:58:25 openat(AT_FDCWD, "/gnu/store/amcs7l0ynj1qg6fp9ll3asiamd4zsq75-m4-1.4.18.lock", O_RDWR|O_CREAT, 0600) = 14
15:58:25 fcntl(14, F_GETFD)             = 0
15:58:25 fcntl(14, F_SETFD, FD_CLOEXEC) = 0
15:58:25 fcntl(14, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:58:25 close(14)                      = 0
15:58:25 openat(AT_FDCWD, "/gnu/store/zvvgr301hz95ac15rp0wsjy5j4cdgkg4-module-import-compiled.lock", O_RDWR|O_CREAT, 0600) = 14
15:58:25 fcntl(14, F_GETFD)             = 0
15:58:25 fcntl(14, F_SETFD, FD_CLOEXEC) = 0
15:58:25 fcntl(14, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:58:25 close(14)                      = 0
15:58:25 openat(AT_FDCWD, "/gnu/store/760kj698c9x1vcmlzk1qr8i9hqw961n3-openssl-1.0.2o-doc.lock", O_RDWR|O_CREAT, 0600) = 14
15:58:25 fcntl(14, F_GETFD)             = 0
15:58:25 fcntl(14, F_SETFD, FD_CLOEXEC) = 0
15:58:25 fcntl(14, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:58:25 close(14)                      = 0
15:58:25 select(445, [15 54 159 177 321 411 414 444], NULL, NULL, {tv_sec=5, tv_usec=0}) = 0 (Timeout)
15:58:30 openat(AT_FDCWD, "/gnu/store/amcs7l0ynj1qg6fp9ll3asiamd4zsq75-m4-1.4.18.lock", O_RDWR|O_CREAT, 0600) = 14
15:58:30 fcntl(14, F_GETFD)             = 0
15:58:30 fcntl(14, F_SETFD, FD_CLOEXEC) = 0
15:58:30 fcntl(14, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:58:30 close(14)                      = 0
15:58:30 openat(AT_FDCWD, "/gnu/store/zvvgr301hz95ac15rp0wsjy5j4cdgkg4-module-import-compiled.lock", O_RDWR|O_CREAT, 0600) = 14
15:58:30 fcntl(14, F_GETFD)             = 0
15:58:30 fcntl(14, F_SETFD, FD_CLOEXEC) = 0
15:58:30 fcntl(14, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:58:30 close(14)                      = 0
15:58:30 openat(AT_FDCWD, "/gnu/store/760kj698c9x1vcmlzk1qr8i9hqw961n3-openssl-1.0.2o-doc.lock", O_RDWR|O_CREAT, 0600) = 14
15:58:30 fcntl(14, F_GETFD)             = 0
15:58:30 fcntl(14, F_SETFD, FD_CLOEXEC) = 0
15:58:30 fcntl(14, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:58:30 close(14)                      = 0
15:58:30 select(445, [15 54 159 177 321 411 414 444], NULL, NULL, {tv_sec=5, tv_usec=0}^Cstrace: Process 20503 detached
$ sudo strace -p 20501 -t
strace: Process 20501 attached
15:59:09 select(121, [20 30 120], NULL, NULL, {tv_sec=0, tv_usec=535316}) = 0 (Timeout)
15:59:10 openat(AT_FDCWD, "/gnu/store/ghc9vcc8ydv305jz0spd73qrrf30gxik-binutils-bootstrap-0.lock", O_RDWR|O_CREAT, 0600) = 8
15:59:10 fcntl(8, F_GETFD)              = 0
15:59:10 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:59:10 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:59:10 close(8)                       = 0
15:59:10 openat(AT_FDCWD, "/gnu/store/5hdpffkgkfszpsin2ir50zscz06x0mb5-coreutils-8.29-debug.lock", O_RDWR|O_CREAT, 0600) = 8
15:59:10 fcntl(8, F_GETFD)              = 0
15:59:10 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:59:10 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:59:10 close(8)                       = 0
15:59:10 openat(AT_FDCWD, "/gnu/store/aasfcliv85frq3aawpa4rw18nvlvl735-gettext-minimal-0.19.8.1.lock", O_RDWR|O_CREAT, 0600) = 8
15:59:10 fcntl(8, F_GETFD)              = 0
15:59:10 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:59:10 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:59:10 close(8)                       = 0
15:59:10 openat(AT_FDCWD, "/gnu/store/j1kpzcpi1m1ihzwyqb60zd4s74yp85g8-glibc-bootstrap-0.lock", O_RDWR|O_CREAT, 0600) = 8
15:59:10 fcntl(8, F_GETFD)              = 0
15:59:10 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:59:10 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:59:10 close(8)                       = 0
15:59:10 openat(AT_FDCWD, "/gnu/store/4llnxsgr6mxxj6pk21d9vbwaxnkbn99k-gnutls-3.5.18-doc.lock", O_RDWR|O_CREAT, 0600) = 8
15:59:10 fcntl(8, F_GETFD)              = 0
15:59:10 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:59:10 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:59:10 close(8)                       = 0
15:59:10 openat(AT_FDCWD, "/gnu/store/7rs9qx86f2w4hjbf9wjm10k4m2vvlbyv-groff-1.22.3-doc.lock", O_RDWR|O_CREAT, 0600) = 8
15:59:10 fcntl(8, F_GETFD)              = 0
15:59:10 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:59:10 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:59:10 close(8)                       = 0
15:59:10 openat(AT_FDCWD, "/gnu/store/d645d919gp1zk8v65qa2r4ia5x1c5n6k-libstdc++-5.5.0.lock", O_RDWR|O_CREAT, 0600) = 8
15:59:10 fcntl(8, F_GETFD)              = 0
15:59:10 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:59:10 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:59:10 close(8)                       = 0
15:59:10 openat(AT_FDCWD, "/gnu/store/p262qk7zsd2wnlal6x1jax2xbqvdddqq-m4-1.4.18.lock", O_RDWR|O_CREAT, 0600) = 8
15:59:10 fcntl(8, F_GETFD)              = 0
15:59:10 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
15:59:10 fcntl(8, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Risurco dumtempe ne disponeblas)
15:59:10 close(8)                       = 0
15:59:10 select(121, [20 30 120], NULL, NULL, {tv_sec=5, tv_usec=0}^Cstrace: Process 20501 detached
$ sudo lsof | grep '/gnu/store/.*\.lock'
guix-daem 20501             root   14uW     REG              253,0          0    3150879 /gnu/store/zvvgr301hz95ac15rp0wsjy5j4cdgkg4-module-import-compiled.lock
guix-daem 20501             root   26uW     REG              253,0          0    3212618 /gnu/store/760kj698c9x1vcmlzk1qr8i9hqw961n3-openssl-1.0.2o-doc.lock
guix-daem 20501             root  116uW     REG              253,0          0    3212684 /gnu/store/amcs7l0ynj1qg6fp9ll3asiamd4zsq75-m4-1.4.18.lock
guix-daem 20503             root    8uW     REG              253,0          0    3212520 /gnu/store/7rs9qx86f2w4hjbf9wjm10k4m2vvlbyv-groff-1.22.3-doc.lock
guix-daem 20503             root   50uW     REG              253,0          0    3212514 /gnu/store/ghc9vcc8ydv305jz0spd73qrrf30gxik-binutils-bootstrap-0.lock
guix-daem 20503             root  155uW     REG              253,0          0    3212547 /gnu/store/j1kpzcpi1m1ihzwyqb60zd4s74yp85g8-glibc-bootstrap-0.lock
guix-daem 20503             root  173uW     REG              253,0          0    3212552 /gnu/store/4llnxsgr6mxxj6pk21d9vbwaxnkbn99k-gnutls-3.5.18-doc.lock
guix-daem 20503             root  317uW     REG              253,0          0    3212602 /gnu/store/d645d919gp1zk8v65qa2r4ia5x1c5n6k-libstdc++-5.5.0.lock
guix-daem 20503             root  407uW     REG              253,0          0    3212655 /gnu/store/5hdpffkgkfszpsin2ir50zscz06x0mb5-coreutils-8.29-debug.lock
guix-daem 20503             root  410uW     REG              253,0          0    3212659 /gnu/store/aasfcliv85frq3aawpa4rw18nvlvl735-gettext-minimal-0.19.8.1.lock
guix-daem 20503             root  440uW     REG              253,0          0    3212686 /gnu/store/p262qk7zsd2wnlal6x1jax2xbqvdddqq-m4-1.4.18.lock
--8<---------------cut here---------------end--------------->8---

So for example:

  • 20501 tries to acquire
    aasfcliv85frq3aawpa4rw18nvlvl735-gettext-minimal-0.19.8.1.lock,
    which is held by 20503;

  • 20503 tries to acquire
    amcs7l0ynj1qg6fp9ll3asiamd4zsq75-m4-1.4.18.lock, which is held by
    20501.

This comes from the fact that ‘LocalStore::buildPaths’ takes the
user-supplied derivation list as is, without sorting it, and then
acquires locks in that order in ‘Worker::run’.

A topological sort (or maybe an alphanumeric sort?) should allow us to
guarantee that guix-daemon processes take locks in the same order, and
then don’t end up in a deadlock.

I discovered this bug while monitoring Cuirass on berlin: several
sessions submit batches of 200 derivations in ‘build-paths’ RPCs, and
sometimes most of the corresponding guix-daemon processes would end up
being stuck in a lock-acquiring loop.

Ludo’.

Severity set to 'important' from 'normal' Request was from ludo@gnu.org (Ludovic Courtès) to control@debbugs.gnu.org. (Mon, 11 Jun 2018 15:43:02 GMT) (full text, mbox, link).

Information forwarded to bug-guix@gnu.org:
bug#31785; Package guix. (Fri, 06 Sep 2019 09:06:01 GMT) (full text, mbox, link).

Message #10 received at 31785@debbugs.gnu.org (full text, mbox, reply):

Here’s another example from berlin today:

--8<---------------cut here---------------start------------->8---
ludo@berlin$ sudo guix processes
SessionPID: 38649
ClientPID: 38611
ClientCommand: /gnu/store/7x9lrzs2l00mfcr3ya7hg1i06i7lq9pd-profile/bin/guile \ /home/mbakke/guix/master/scripts/guix build --no-grafts --keep-going --max-silent-time=36000 --timeout=216000 -s armhf-linux nmoldyn r-msnid r-yamss netcdf-fortran python-netcdf4
LockHeld: /gnu/store/v6hcm1gvv3gdfbnq6cd4kn1i6ip3y74s-netcdf-fortran-4.4.4.lock
LockHeld: /gnu/store/ydxl0ws9kk6ix58m99ib7qhi157yq49h-r-msnid-1.18.1.lock
ChildProcess: 33181: /gnu/store/9alic3caqhay3h8mx4iihpmyj6ymqpcx-guile-2.2.4/bin/guile \ /gnu/store/vyhfp0gj4rx74yw0ybalzj8bvmqgp9pr-guix-1.0.1-4.c902458/bin/.guix-real offload x86_64-linux 36000 1 216000

[...]

SessionPID: 44043
ClientPID: 44023
ClientCommand: /gnu/store/7x9lrzs2l00mfcr3ya7hg1i06i7lq9pd-profile/bin/guile \ /home/mbakke/guix/master/scripts/guix build --no-grafts --keep-going --max-silent-time=36000 --timeout=216000 -s armhf-linux netcdf-fortran r-msnid nmoldyn r-yamss
LockHeld: /gnu/store/69jjabypcpx83482rh3yp4a9ncjimw6b-r-yamss-1.10.0.lock
LockHeld: /gnu/store/ibdbwxb1i8yal8ilqxxgnzh6bxpinic1-nmoldyn-3.0.11.lock
ChildProcess: 48997: /gnu/store/9alic3caqhay3h8mx4iihpmyj6ymqpcx-guile-2.2.4/bin/guile \ /gnu/store/vyhfp0gj4rx74yw0ybalzj8bvmqgp9pr-guix-1.0.1-4.c902458/bin/.guix-real offload x86_64-linux 36000 1 216000

ludo@berlin ~$ sudo strace -p 38649 -e openat,fcntl
strace: Process 38649 attached
openat(AT_FDCWD, "/gnu/store/ibdbwxb1i8yal8ilqxxgnzh6bxpinic1-nmoldyn-3.0.11.lock", O_RDWR|O_CREAT, 0600) = 10
fcntl(10, F_GETFD)                      = 0
fcntl(10, F_SETFD, FD_CLOEXEC)          = 0
fcntl(10, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Resource temporarily unavailable)
openat(AT_FDCWD, "/gnu/store/69jjabypcpx83482rh3yp4a9ncjimw6b-r-yamss-1.10.0.lock", O_RDWR|O_CREAT, 0600) = 10
fcntl(10, F_GETFD)                      = 0
fcntl(10, F_SETFD, FD_CLOEXEC)          = 0
fcntl(10, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Resource temporarily unavailable)
^Cstrace: Process 38649 detached

ludo@berlin ~$ sudo strace -p 44043 -e openat,fcntl
strace: Process 44043 attached
openat(AT_FDCWD, "/gnu/store/ydxl0ws9kk6ix58m99ib7qhi157yq49h-r-msnid-1.18.1.lock", O_RDWR|O_CREAT, 0600) = 10
fcntl(10, F_GETFD)                      = 0
fcntl(10, F_SETFD, FD_CLOEXEC)          = 0
fcntl(10, F_SETLK, {l_type=F_WRLCK, l_whence=SEEK_SET, l_start=0, l_len=0}) = -1 EAGAIN (Resource temporarily unavailable)
^Cstrace: Process 44043 detached
--8<---------------cut here---------------end--------------->8---

A very palpable deadlock.

Ludo’.

Information forwarded to bug-guix@gnu.org:
bug#31785; Package guix. (Wed, 04 Nov 2020 15:22:02 GMT) (full text, mbox, link).

Message #13 received at 31785@debbugs.gnu.org (full text, mbox, reply):

Hi,

ludo@gnu.org (Ludovic Courtès) skribis:

> This comes from the fact that ‘LocalStore::buildPaths’ takes the
> user-supplied derivation list as is, without sorting it, and then
> acquires locks in that order in ‘Worker::run’.

This diagnostic is incorrect: ‘Goals’ is a set sorted according to
‘CompareGoalPtrs’, which is lexical sort that arranges so substitution
goals come before derivation goals.  Thus, ‘_topGoals’ and ‘awake2’ in
Worker::run are sorted in a deterministic fashion.


The problem is that ‘Worker::waitForAWhile’ reshuffles the order of
goals by temporarily moving goals out of the way.  This can happen when
offloading replies “postpone”, which is inherently non-deterministic
(which goals are put to sleep will vary from one session to another
session.)

When those goals are eventually woken up from ‘Worker::waitForInput’,
they’re reprocessed, in sorted order, but potentially with “holes”
compared to other ‘guix-daemon’ processes.

That’s only a partial explanation; we need to go further to come up with
an actual deadlock scenario.

Ludo’.

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