Re: [BUG] selftest: memfd: indefinite hang in ./fuse_mnt ./mnt

From: Mirsad Todorovac
Date: Sat Mar 09 2024 - 12:13:34 EST

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On 2/27/24 14:52, Mirsad Todorovac wrote:

Hi everybody,

This is an issue already reported in thread:

Link: https://lore.kernel.org/all/4a5aa618-8fbc-4053-ba38-0809735d864b@xxxxxxxxxxxx/

around January 7th.

It is again against the latest vanilla torvalds build on Ubuntu 23.10 and
an AMD Ryzen 7 box.

Please find the .config attached.

Here are some diagnostics and log outputs:

root@stargazer:/home/marvin/linux/kernel/linux_torvalds# lsof -p 85021
lsof: WARNING: can't stat() fuse.portal file system /run/user/1000/doc
      Output information may be incomplete.
lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs
      Output information may be incomplete.
COMMAND    PID USER   FD   TYPE DEVICE SIZE/OFF    NODE NAME
fuse_mnt 85021 root cwd    DIR 259,13     4096       2 /
fuse_mnt 85021 root rtd    DIR 259,13     4096       2 /
fuse_mnt 85021 root txt    REG   0,44    16760 7558526 /home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/memfd/fuse_mnt
fuse_mnt 85021 root mem    REG   0,40          7558526 /home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/memfd/fuse_mnt (path dev=0,44)
fuse_mnt 85021 root mem    REG   0,26           481843 /usr/lib/x86_64-linux-gnu/libc.so.6 (path dev=0,27)
fuse_mnt 85021 root mem    REG   0,26           434443 /usr/lib/x86_64-linux-gnu/libfuse.so.2.9.9 (path dev=0,27)
fuse_mnt 85021 root mem    REG   0,26            22118 /usr/libexec/coreutils/libstdbuf.so (path dev=0,27)
fuse_mnt 85021 root mem    REG   0,26           481840 /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 (path dev=0,27)
fuse_mnt 85021 root    0u   CHR    1,3      0t0       5 /dev/null
fuse_mnt 85021 root    1u   CHR    1,3      0t0       5 /dev/null
fuse_mnt 85021 root    2u   CHR    1,3      0t0       5 /dev/null
fuse_mnt 85021 root    3w FIFO   0,14      0t0 404306 pipe
fuse_mnt 85021 root    4w FIFO   0,14      0t0   19072 pipe
fuse_mnt 85021 root    5u   CHR 10,229      0t0      88 /dev/fuse
root@stargazer:/home/marvin/linux/kernel/linux_torvalds# strace -p !$
strace -p 85021
strace: Process 85021 attached
futex(0x7ffc1a7c9ea0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, FUTEX_BITSET_MATCH_ANY^Cstrace: Process 85021 detached
<detached ...>

root@stargazer:/home/marvin/linux/kernel/linux_torvalds#

make[3]: Entering directory '/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/memfd'
TAP version 13
1..3
# timeout set to 45
# selftests: memfd: memfd_test
# memfd: CREATE
# memfd: BASIC
# memfd: SEAL-EXEC
# memfd:        Apply SEAL_EXEC
# memfd:        Apply ALL_SEALS
# memfd: EXEC_NO_SEAL
# memfd: NOEXEC_SEAL
# memfd: SEAL-WRITE
# memfd: SEAL-FUTURE-WRITE
# memfd: SEAL-SHRINK
# memfd: SEAL-GROW
# memfd: SEAL-RESIZE
# memfd: sysctl 0
# memfd: sysctl 1
# memfd: sysctl 0
# memfd: sysctl 2
# memfd: sysctl 1
# memfd: sysctl 0
# memfd: nested sysctl 0
# memfd: sysctl 0
# memfd: sysctl 1
# memfd: sysctl 0
# memfd: sysctl 2
# memfd: sysctl 1
# memfd: sysctl 0
# memfd: nested sysctl 1
# memfd: nested sysctl 2
# memfd: nested sysctl 0 -> 1 after fork
# memfd: nested sysctl 0 -> 2 after fork
# memfd: nested sysctl 2 -> 1 after fork
# memfd: nested sysctl 2 -> 0 after fork
# memfd: nested sysctl 1 -> 0 after fork
# memfd: SHARE-DUP
# memfd: SHARE-MMAP
# memfd: SHARE-OPEN
# memfd: SHARE-FORK
# memfd: SHARE-DUP (shared file-table)
# memfd: SHARE-MMAP (shared file-table)
# memfd: SHARE-OPEN (shared file-table)
# memfd: SHARE-FORK (shared file-table)
# memfd: DONE
ok 1 selftests: memfd: memfd_test
# timeout set to 45
# selftests: memfd: run_fuse_test.sh
# opening: ./mnt/memfd
# fuse: DONE
ok 2 selftests: memfd: run_fuse_test.sh
# timeout set to 45
# selftests: memfd: run_hugetlbfs_test.sh
# memfd-hugetlb: CREATE
# memfd-hugetlb: BASIC
# memfd-hugetlb: SEAL-EXEC
# memfd-hugetlb:        Apply SEAL_EXEC
# fchmod(/memfd:kern_memfd_seal_exec (deleted), 00777) didn't fail as expected
# ./run_hugetlbfs_test.sh: line 60: 85016 Aborted                 (core dumped) ./memfd_test hugetlbfs
# opening: ./mnt/memfd
# ADD_SEALS(6, 0 -> 8) failed: Device or resource busy
# 8 != 0 = GET_SEALS(6)
# Aborted (core dumped)
ok 3 selftests: memfd: run_hugetlbfs_test.sh
make[3]: Leaving directory '/home/marvin/linux/kernel/linux_torvalds/tools/testing/selftests/memfd'

As this bug report did not receive much attention, I did a little digging myself, so the debug
version of the run is like this:

root@tools/testing/selftests/memfd# gdb ./memfd_test
GNU gdb (Ubuntu 12.1-0ubuntu1~22.04.1) 12.1
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./memfd_test...
(gdb) run hugetlbfs
Starting program: tools/testing/selftests/memfd/memfd_test hugetlbfs
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
memfd-hugetlb: CREATE
memfd-hugetlb: BASIC
memfd-hugetlb: SEAL-EXEC
memfd-hugetlb: Apply SEAL_EXEC
fchmod(/memfd:kern_memfd_seal_exec (deleted), 00777) didn't fail as expected

Program received signal SIGABRT, Aborted.
__pthread_kill_implementation (no_tid=0, signo=6, threadid=140737353742144) at ./nptl/pthread_kill.c:44
44 ./nptl/pthread_kill.c: No such file or directory.
(gdb) bt
#0 __pthread_kill_implementation (no_tid=0, signo=6, threadid=140737353742144) at ./nptl/pthread_kill.c:44
#1 __pthread_kill_internal (signo=6, threadid=140737353742144) at ./nptl/pthread_kill.c:78
#2 __GI___pthread_kill (threadid=140737353742144, signo=signo@entry=6) at ./nptl/pthread_kill.c:89
#3 0x00007ffff7c42476 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#4 0x00007ffff7c287f3 in __GI_abort () at ./stdlib/abort.c:79
#5 0x0000555555556de7 in mfd_fail_chmod (fd=3, mode=511) at memfd_test.c:746
#6 0x0000555555557834 in test_exec_seal () at memfd_test.c:1090
#7 0x0000555555558934 in main (argc=2, argv=0x7fffffffe368) at memfd_test.c:1594
(gdb) list memfd_test.c:1594
1589 }
1590 }
1591
1592 test_create();
1593 test_basic();
→ 1594 test_exec_seal();
1595 test_exec_no_seal();
1596 test_noexec_seal();
1597
1598 test_seal_write();
(gdb)

##############################
### NOTE!!!
##############################

The memfd file is impossible to remove using the unlink() syscall. I am not certain if this
is an error or deliberate design feature:

unlinkat(AT_FDCWD, "mnt/memfd", 0) = -1 ENOSYS (Function not implemented)

##############################
### NOTE!!!
##############################

--------------------------------------------------------------------------------------------------

Additionally, debugging memfd F_SEAL_WRITE:

root@defiant:tools/testing/selftests/memfd# gdb ./fuse_test
GNU gdb (Ubuntu 12.1-0ubuntu1~22.04.1) 12.1
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./fuse_test...
(gdb) run ./mnt/memfd hugetlbfs
Starting program: tools/testing/selftests/memfd/fuse_test ./mnt/memfd hugetlbfs
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
opening: ./mnt/memfd
[Detaching after fork from child process 1301253]
ADD_SEALS(4, 0 -> 8) failed: Device or resource busy
8 != 0 = GET_SEALS(4)

Program received signal SIGABRT, Aborted.
__pthread_kill_implementation (no_tid=0, signo=6, threadid=140737353742144) at ./nptl/pthread_kill.c:44
44 ./nptl/pthread_kill.c: No such file or directory.
(gdb) bt
#0 __pthread_kill_implementation (no_tid=0, signo=6, threadid=140737353742144) at ./nptl/pthread_kill.c:44
#1 __pthread_kill_internal (signo=6, threadid=140737353742144) at ./nptl/pthread_kill.c:78
#2 __GI___pthread_kill (threadid=140737353742144, signo=signo@entry=6) at ./nptl/pthread_kill.c:89
#3 0x00007ffff7c42476 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#4 0x00007ffff7c287f3 in __GI_abort () at ./stdlib/abort.c:79
#5 0x00005555555555a2 in mfd_assert_has_seals (fd=4, seals=8) at fuse_test.c:85
#6 0x0000555555555abd in main (argc=3, argv=0x7fffffffe358) at fuse_test.c:303
(gdb) list fuse_test.c:303
298 was_sealed = mfd_assert_get_seals(mfd) & F_SEAL_WRITE;
299
300 /* Wait for sealing-thread to finish and verify that it
301 * successfully sealed the file after the second try. */
302 join_sealing_thread(pid);
→ 303 mfd_assert_has_seals(mfd, F_SEAL_WRITE);
304
305 /* *IF* the memfd-object was sealed at the time our read() returned,
306 * then the kernel did a page-replacement or canceled the read() (or
307 * whatever magic it did..). In that case, the memfd object is still
(gdb)

strace output might give some more light on the issue:

root@tools/testing/selftests/memfd# strace -f ./fuse_test ./mnt/memfd hugetlbfs
execve("./fuse_test", ["./fuse_test", "./mnt/memfd", "hugetlbfs"], 0x7ffedde36ba8 /* 33 vars */) = 0
brk(NULL) = 0x5596294a2000
arch_prctl(0x3001 /* ARCH_??? */, 0x7fff07c45f50) = -1 EINVAL (Invalid argument)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7de66999c000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=101071, ...}, AT_EMPTY_PATH) = 0
mmap(NULL, 101071, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7de669983000
close(3) = 0
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\237\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
pread64(3, "\4\0\0\0 \0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0"..., 48, 848) = 48
pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\302\211\332Pq\2439\235\350\223\322\257\201\326\243\f"..., 68, 896) = 68
newfstatat(3, "", {st_mode=S_IFREG|0755, st_size=2220400, ...}, AT_EMPTY_PATH) = 0
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
mmap(NULL, 2264656, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7de669600000
mprotect(0x7de669628000, 2023424, PROT_NONE) = 0
mmap(0x7de669628000, 1658880, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x28000) = 0x7de669628000
mmap(0x7de6697bd000, 360448, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bd000) = 0x7de6697bd000
mmap(0x7de669816000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x215000) = 0x7de669816000
mmap(0x7de66981c000, 52816, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7de66981c000
close(3) = 0
mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7de669980000
arch_prctl(ARCH_SET_FS, 0x7de669980740) = 0
set_tid_address(0x7de669980a10) = 1301385
set_robust_list(0x7de669980a20, 24) = 0
rseq(0x7de6699810e0, 0x20, 0, 0x53053053) = 0
mprotect(0x7de669816000, 16384, PROT_READ) = 0
mprotect(0x559628558000, 4096, PROT_READ) = 0
mprotect(0x7de6699d6000, 8192, PROT_READ) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
munmap(0x7de669983000, 101071) = 0
getrandom("\x5a\x3b\xfe\xc5\x49\xcb\x6b\xc2", 8, GRND_NONBLOCK) = 8
brk(NULL) = 0x5596294a2000
brk(0x5596294c3000) = 0x5596294c3000
openat(AT_FDCWD, "/proc/meminfo", O_RDONLY) = 3
newfstatat(3, "", {st_mode=S_IFREG|0444, st_size=0, ...}, AT_EMPTY_PATH) = 0
read(3, "MemTotal: 64906640 kB\nMemF"..., 1024) = 1024
read(3, " 121580 kB\nVmallocChunk: "..., 1024) = 507
close(3) = 0
mmap(NULL, 4198400, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7de669000000
newfstatat(1, "", {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x3), ...}, AT_EMPTY_PATH) = 0
write(1, "opening: ./mnt/memfd\n", 21opening: ./mnt/memfd
) = 21
openat(AT_FDCWD, "./mnt/memfd", O_RDONLY|O_CLOEXEC) = 3
memfd_create("kern_memfd_fuse", MFD_CLOEXEC|MFD_ALLOW_SEALING|MFD_HUGETLB) = 4
ftruncate(4, 4194304) = 0
mmap(NULL, 4194304, PROT_READ|PROT_WRITE, MAP_SHARED, 4, 0) = 0x7de668c00000
clone(child_stack=0x5596294b2900, flags=CLONE_VM|CLONE_FS|CLONE_FILES|SIGCHLDstrace: Process 1301386 attached
) = 1301386
[pid 1301385] read(3, <unfinished ...>
[pid 1301386] clock_nanosleep(CLOCK_REALTIME, 0, {tv_sec=0, tv_nsec=200000000}, NULL) = 0
[pid 1301386] munmap(0x7de668c00000, 4194304) = 0
[pid 1301386] fcntl(4, F_GET_SEALS) = 0
[pid 1301386] fcntl(4, F_ADD_SEALS, F_SEAL_WRITE) = -1 EBUSY (Device or resource busy)
[pid 1301386] clock_nanosleep(CLOCK_REALTIME, 0, {tv_sec=1, tv_nsec=0}, <unfinished ...>
[pid 1301385] <... read resumed>0x7de668c00000, 4194304) = 21
[pid 1301385] fcntl(4, F_GET_SEALS) = 0
[pid 1301385] wait4(1301386, <unfinished ...>
[pid 1301386] <... clock_nanosleep resumed>0x5596294b28a0) = 0
[pid 1301386] fcntl(4, F_GET_SEALS) = 0
[pid 1301386] fcntl(4, F_ADD_SEALS, F_SEAL_WRITE) = -1 EBUSY (Device or resource busy)
[pid 1301386] write(1, "ADD_SEALS(4, 0 -> 8) failed: Dev"..., 53ADD_SEALS(4, 0 -> 8) failed: Device or resource busy
) = 53
[pid 1301386] rt_sigprocmask(SIG_UNBLOCK, [ABRT], NULL, 8) = 0
[pid 1301386] gettid() = 1301386
[pid 1301386] getpid() = 1301386
[pid 1301386] tgkill(1301386, 1301386, SIGABRT) = 0
[pid 1301386] --- SIGABRT {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=1301386, si_uid=0} ---
[pid 1301386] +++ killed by SIGABRT (core dumped) +++
<... wait4 resumed>NULL, 0, NULL) = 1301386
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_DUMPED, si_pid=1301386, si_uid=0, si_status=SIGABRT, si_utime=0, si_stime=0} ---
fcntl(4, F_GET_SEALS) = 0
write(1, "8 != 0 = GET_SEALS(4)\n", 228 != 0 = GET_SEALS(4)
) = 22
rt_sigprocmask(SIG_UNBLOCK, [ABRT], NULL, 8) = 0
gettid() = 1301385
getpid() = 1301385
tgkill(1301385, 1301385, SIGABRT) = 0
--- SIGABRT {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=1301385, si_uid=0} ---
+++ killed by SIGABRT (core dumped) +++
Aborted (core dumped)
root@tools/testing/selftests/memfd#

----------------------

Without "hugetlbfs" argument, the program finishes with "fuse: DONE":

root@defiant:/home/marvin/linux/kernel/net-next/tools/testing/selftests/memfd# ./fuse_test ./mnt/memfd
opening: ./mnt/memfd
fuse: DONE
root@defiant:/home/marvin/linux/kernel/net-next/tools/testing/selftests/memfd# strace -f ./fuse_test ./mnt/memfd
execve("./fuse_test", ["./fuse_test", "./mnt/memfd"], 0x7ffe52f7eb90 /* 33 vars */) = 0
brk(NULL) = 0x63d5e57ff000
arch_prctl(0x3001 /* ARCH_??? */, 0x7ffd9ce0ada0) = -1 EINVAL (Invalid argument)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x70cd31796000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=101071, ...}, AT_EMPTY_PATH) = 0
mmap(NULL, 101071, PROT_READ, MAP_PRIVATE, 3, 0) = 0x70cd3177d000
close(3) = 0
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\237\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
pread64(3, "\4\0\0\0 \0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0"..., 48, 848) = 48
pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\302\211\332Pq\2439\235\350\223\322\257\201\326\243\f"..., 68, 896) = 68
newfstatat(3, "", {st_mode=S_IFREG|0755, st_size=2220400, ...}, AT_EMPTY_PATH) = 0
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
mmap(NULL, 2264656, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x70cd31400000
mprotect(0x70cd31428000, 2023424, PROT_NONE) = 0
mmap(0x70cd31428000, 1658880, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x28000) = 0x70cd31428000
mmap(0x70cd315bd000, 360448, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bd000) = 0x70cd315bd000
mmap(0x70cd31616000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x215000) = 0x70cd31616000
mmap(0x70cd3161c000, 52816, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x70cd3161c000
close(3) = 0
mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x70cd3177a000
arch_prctl(ARCH_SET_FS, 0x70cd3177a740) = 0
set_tid_address(0x70cd3177aa10) = 1301750
set_robust_list(0x70cd3177aa20, 24) = 0
rseq(0x70cd3177b0e0, 0x20, 0, 0x53053053) = 0
mprotect(0x70cd31616000, 16384, PROT_READ) = 0
mprotect(0x63d5e3a98000, 4096, PROT_READ) = 0
mprotect(0x70cd317d0000, 8192, PROT_READ) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
munmap(0x70cd3177d000, 101071) = 0
getrandom("\x8d\xcf\x51\x91\x51\xe1\xdc\xcb", 8, GRND_NONBLOCK) = 8
brk(NULL) = 0x63d5e57ff000
brk(0x63d5e5820000) = 0x63d5e5820000
newfstatat(1, "", {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x3), ...}, AT_EMPTY_PATH) = 0
write(1, "opening: ./mnt/memfd\n", 21opening: ./mnt/memfd
) = 21
openat(AT_FDCWD, "./mnt/memfd", O_RDONLY|O_CLOEXEC) = 3
memfd_create("kern_memfd_fuse", MFD_CLOEXEC|MFD_ALLOW_SEALING) = 4
ftruncate(4, 8192) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_SHARED, 4, 0) = 0x70cd31794000
clone(child_stack=0x63d5e58116b0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|SIGCHLDstrace: Process 1301751 attached
) = 1301751
[pid 1301750] read(3, <unfinished ...>
[pid 1301751] clock_nanosleep(CLOCK_REALTIME, 0, {tv_sec=0, tv_nsec=200000000}, NULL) = 0
[pid 1301751] munmap(0x70cd31794000, 8192) = 0
[pid 1301751] fcntl(4, F_GET_SEALS) = 0
[pid 1301751] fcntl(4, F_ADD_SEALS, F_SEAL_WRITE) = -1 EBUSY (Device or resource busy)
[pid 1301751] clock_nanosleep(CLOCK_REALTIME, 0, {tv_sec=1, tv_nsec=0}, <unfinished ...>
[pid 1301750] <... read resumed>0x70cd31794000, 8192) = 21
[pid 1301750] fcntl(4, F_GET_SEALS) = 0
[pid 1301750] wait4(1301751, <unfinished ...>
[pid 1301751] <... clock_nanosleep resumed>0x63d5e5811650) = 0
[pid 1301751] fcntl(4, F_GET_SEALS) = 0
[pid 1301751] fcntl(4, F_ADD_SEALS, F_SEAL_WRITE) = 0
[pid 1301751] exit(0) = ?
[pid 1301751] +++ exited with 0 +++
<... wait4 resumed>NULL, 0, NULL) = 1301751
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=1301751, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
fcntl(4, F_GET_SEALS) = 0x8 (seals F_SEAL_WRITE)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE, 4, 0) = 0x70cd31794000
close(4) = 0
close(3) = 0
write(1, "fuse: DONE\n", 11fuse: DONE
) = 11
exit_group(0) = ?
+++ exited with 0 +++
root@defiant:/home/marvin/linux/kernel/net-next/tools/testing/selftests/memfd#

-------------------------------------

I hope this will attract any attention. Apparently, the bug is connected with hugetlbfs memfd,
and it fails even when I manually allocated 10 hugetlbfs pages due to non-transparent reasons.

My knowledge of memfd interface is insufficient to solve this problem, and the variant
w/o use of hugetlbfs apparently works.

Thank you.

Best regards,
Mirsad Todorovac

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