Details
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Bug
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Resolution: Fixed
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Major
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None
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None
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3
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9223372036854775807
Description
On attempting to set up some read-only bind mounts on nodes in order to provide pseudo isolation within the single namespace of a Lustre FS, the following issue is seen.
After the read-only bind mount is created on Lustre mount /work, files can still be created. Although the created file cannot be written to:
Set up the bind mount using /work:
# mount --bind /work /tmp/bind_ro/ # mount -o remount,ro /tmp/bind_ro/ # mount | grep bind_ro /work on /tmp/bind_ro type none (ro,bind)
Touch a file that does not exist, which yields an error.
# touch /tmp/bind_ro/gbrown touch: cannot touch `/tmp/bind_ro/gbrown': Read-only file system
It would be expected that the preceding 'touch' did not create a file.
However, a file was created:
ls -l /tmp/bind_ro/gbrown -rw-r--r-- 1 root root 0 Sep 9 13:59 /tmp/bind_ro/gbrown
Though the file was created, it cannot be written to:
We can't write data to the file, the cat below returns no output. # echo foo > /tmp/bind_ro/gbrown -bash: /tmp/bind_ro/gbrown: Read-only file system # cat /tmp/bind_ro/gbrown
Comparatively, no file is created when the read-only bind mount is executed on NFS::
# mount --bind /cm/shared/ /tmp/bind_ro/ # mount -o remount,ro /tmp/bind_ro/ # touch /tmp/bind_ro/gbrown touch: cannot touch `/tmp/bind_ro/gbrown': Read-only file system # ls -l /tmp/bind_ro/gbrown ls: cannot access /tmp/bind_ro/gbrown: No such file or directory
The following are strace excerpts comparing the 'touch' process between Lustre and NFS:
Attempting to touch a file within a read-only bind mount of a Lustre FS.
# strace -v -s 1024 touch foobar 2>&1 | tee /tmp/strace_lustre.out
...
futex(0x7fffffff925c, FUTEX_WAKE_PRIVATE, 1) = 0
futex(0x7fffffff925c, 0x189 /* FUTEX_??? */, 1, NULL, 2aaaab470700) = -1 EAGAIN (Resource temporarily unavailable)
rt_sigaction(SIGRTMIN, {0x2aaaab2588f0, [], SA_RESTORER|SA_SIGINFO, 0x2aaaab262850}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {0x2aaaab258980, [], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x2aaaab262850}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
brk(0) = 0x60e000
brk(0x62f000) = 0x62f000
open("foobar", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666) = -1 EROFS (Read-only file system)
utimensat(AT_FDCWD, "foobar", NULL, 0) = -1 EROFS (Read-only file system)
write(2, "touch: ", 7touch: ) = 7
write(2, "cannot touch `foobar'", 21cannot touch `foobar') = 21
write(2, ": Read-only file system", 23: Read-only file system) = 23
write(2, "\n", 1
) = 1
close(1) = 0
close(2) = 0
exit_group(1) = ?
File is created.
# stat foobar File: `foobar' Size: 0 Blocks: 0 IO Block: 4194304 regular empty file Device: 886a9b20h/2288687904d Inode: 144116072587526409 Links: 1 Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root) Access: 2016-09-21 07:51:29.000000000 +0000 Modify: 2016-09-21 07:51:29.000000000 +0000 Change: 2016-09-21 07:51:29.000000000 +0000 Birth: -
Attempting to touch a file within a read-only bind mount of a NFS FS.
# strace -v -s 1024 touch foobar 2>&1 | tee /tmp/strace_nfs.out
...
futex(0x7fffffff925c, FUTEX_WAKE_PRIVATE, 1) = 0
futex(0x7fffffff925c, 0x189 /* FUTEX_??? */, 1, NULL, 2aaaab470700) = -1 EAGAIN (Resource temporarily unavailable)
rt_sigaction(SIGRTMIN, {0x2aaaab2588f0, [], SA_RESTORER|SA_SIGINFO, 0x2aaaab262850}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {0x2aaaab258980, [], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x2aaaab262850}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
brk(0) = 0x60e000
brk(0x62f000) = 0x62f000
open("foobar", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666) = -1 EROFS (Read-only file system)
utimensat(AT_FDCWD, "foobar", NULL, 0) = -1 ENOENT (No such file or directory)
write(2, "touch: ", 7touch: ) = 7
write(2, "cannot touch `foobar'", 21cannot touch `foobar') = 21
write(2, ": Read-only file system", 23: Read-only file system) = 23
write(2, "\n", 1
) = 1
close(1) = 0
close(2) = 0
exit_group(1) = ?
File is not created.
# stat foobar stat: cannot stat `foobar': No such file or directory