git push locks up forever, file protocol

git push locks up forever, file protocol

[Jason Morgan]

Hi,

We have a remote repo accessed using the 'file:' protocol, mounted over Samba using drvfs into a WSL2 instance of Ubuntu 20.04.

We find a 'git push' waits forever. git version 2.25.1

Over a local LAN this works fine, but over a VPN this fails, hinting at some sort of race condition.

Output from strace hints that git is trying (and failing) to read from a closed file handle.

Final output from strace:

-----------
openat(AT_FDCWD, ".git/objects/ad/065dad4384ae8c81c120c562985078d1f7b34b", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=152, ...}) = 0
mmap(NULL, 152, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
close(3)                                = 0
munmap(0x7f3e0e4af000, 152)             = 0
openat(AT_FDCWD, ".git/objects/30/2508dfe5201db6c000ebf17b0c69e3afb31218", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0555, st_size=214, ...}) = 0
mmap(NULL, 214, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
close(3)                                = 0
munmap(0x7f3e0e4af000, 214)             = 0
openat(AT_FDCWD, ".git/objects/d2/2323ec2ec40a74fbd519509662254c3cfda206", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=161, ...}) = 0
mmap(NULL, 161, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
close(3)                                = 0
munmap(0x7f3e0e4af000, 161)             = 0
access(".git/hooks/pre-push", X_OK)     = -1 ENOENT (No such file or directory)
write(4, "00953ea50e3c1f49c33f7dbbb5e3a310"..., 149) = 149
write(4, "0000", 4)                     = 4
pipe([3, 6])                            = 0
fcntl(6, F_GETFD)                       = 0
fcntl(6, F_SETFD, FD_CLOEXEC)           = 0
mmap(NULL, 8392704, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7f3e0d641000
mprotect(0x7f3e0d642000, 8388608, PROT_READ|PROT_WRITE) = 0
clone(child_stack=0x7f3e0de40fb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tid=[12802], tls=0x7f3e0de41700, child_tidptr=0x7f3e0de419d0) = 12802
pipe([7, 8])                            = 0
stat("/usr/lib/git-core/git", {st_mode=S_IFREG|0755, st_size=3093072, ...}) = 0
pipe([9, 10])                           = 0
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f3e0e1dae50) = 12803
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
close(10)                               = 0
read(9, "", 8)                          = 0
close(9)                                = 0
close(7)                                = 0
close(4)                                = 0
fcntl(8, F_GETFL)                       = 0x1 (flags O_WRONLY)
openat(AT_FDCWD, ".git/objects/3e", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 4
fstat(4, {st_mode=S_IFDIR|0777, st_size=4096, ...}) = 0
getdents64(4, /* 22 entries */, 32768)  = 1328
getdents64(4, /* 0 entries */, 32768)   = 0
close(4)                                = 0
fstat(8, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
write(8, "^3ea50e3c1f49c33f7dbbb5e3a31017f"..., 83) = 83
close(8)                                = 0
Enumerating objects: 31, done.ts: 1
Counting objects: 100% (31/31), done.
Delta compression using up to 8 threads
Compressing objects: 100% (23/23), done.
Writing objects: 100% (23/23), 5.60 KiB | 212.00 KiB/s, done.
Total 23 (delta 14), reused 0 (delta 0)
[{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 12803
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12803, si_uid=1000, si_status=0, si_utime=2, si_stime=6} ---
read(3,
------------------
That last read from handle 3 (which is closed) lasts forever until you ctrl-c.

The abbreviated strace output, simply halting at the comma, is very odd.

Note the behaviour is the same with the file: protocol prefix and without.

j.

Re: git push locks up forever, file protocol

[brian m. carlson]

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On 2022-04-21 at 08:30:50, Jason Morgan wrote:
> Hi,
> 
> We have a remote repo accessed using the 'file:' protocol, mounted over Samba using drvfs into a WSL2 instance of Ubuntu 20.04.
> 
> We find a 'git push' waits forever. git version 2.25.1

I seem to recall that we've fixed some various issues with protocol
handling in the 2.29 timeframe.  Is it possible you could try 2.36.0 to
see if you can reproduce it there?

Also, it would be interesting to see if there's a difference in
behaviour between setting protocol.version to 0 and setting it to 2.
That might tell us something that would help tracking this down.

> Over a local LAN this works fine, but over a VPN this fails, hinting at some sort of race condition.
>
> Output from strace hints that git is trying (and failing) to read from a closed file handle.

I don't think this is the case.  If Git were trying to read from a
closed file handle, the kernel would immediately return -1 with errno
set to EBADF.  Those operations won't block because there's nothing to
read.

> Final output from strace:
> 
> -----------
> openat(AT_FDCWD, ".git/objects/ad/065dad4384ae8c81c120c562985078d1f7b34b", O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {st_mode=S_IFREG|0444, st_size=152, ...}) = 0
> mmap(NULL, 152, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
> close(3)                                = 0
> munmap(0x7f3e0e4af000, 152)             = 0
> openat(AT_FDCWD, ".git/objects/30/2508dfe5201db6c000ebf17b0c69e3afb31218", O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {st_mode=S_IFREG|0555, st_size=214, ...}) = 0
> mmap(NULL, 214, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
> close(3)                                = 0
> munmap(0x7f3e0e4af000, 214)             = 0
> openat(AT_FDCWD, ".git/objects/d2/2323ec2ec40a74fbd519509662254c3cfda206", O_RDONLY|O_CLOEXEC) = 3
> fstat(3, {st_mode=S_IFREG|0444, st_size=161, ...}) = 0
> mmap(NULL, 161, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
> close(3)                                = 0

FD 3 is closed here...

> munmap(0x7f3e0e4af000, 161)             = 0
> access(".git/hooks/pre-push", X_OK)     = -1 ENOENT (No such file or directory)
> write(4, "00953ea50e3c1f49c33f7dbbb5e3a310"..., 149) = 149
> write(4, "0000", 4)                     = 4
> pipe([3, 6])                            = 0

And then it's recreated here as one part of a pipe, so it isn't closed.

> fcntl(6, F_GETFD)                       = 0
> fcntl(6, F_SETFD, FD_CLOEXEC)           = 0
> mmap(NULL, 8392704, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7f3e0d641000
> mprotect(0x7f3e0d642000, 8388608, PROT_READ|PROT_WRITE) = 0
> clone(child_stack=0x7f3e0de40fb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tid=[12802], tls=0x7f3e0de41700, child_tidptr=0x7f3e0de419d0) = 12802

My guess is that in the child (which isn't shown here) that FD 6 is
hooked up to either standard output or standard error.  You'd need to
follow children to see.

> pipe([7, 8])                            = 0
> stat("/usr/lib/git-core/git", {st_mode=S_IFREG|0755, st_size=3093072, ...}) = 0
> pipe([9, 10])                           = 0
> rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
> clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f3e0e1dae50) = 12803
> rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
> close(10)                               = 0
> read(9, "", 8)                          = 0
> close(9)                                = 0
> close(7)                                = 0
> close(4)                                = 0
> fcntl(8, F_GETFL)                       = 0x1 (flags O_WRONLY)
> openat(AT_FDCWD, ".git/objects/3e", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 4
> fstat(4, {st_mode=S_IFDIR|0777, st_size=4096, ...}) = 0
> getdents64(4, /* 22 entries */, 32768)  = 1328
> getdents64(4, /* 0 entries */, 32768)   = 0
> close(4)                                = 0
> fstat(8, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
> write(8, "^3ea50e3c1f49c33f7dbbb5e3a31017f"..., 83) = 83
> close(8)                                = 0
> Enumerating objects: 31, done.ts: 1
> Counting objects: 100% (31/31), done.
> Delta compression using up to 8 threads
> Compressing objects: 100% (23/23), done.
> Writing objects: 100% (23/23), 5.60 KiB | 212.00 KiB/s, done.
> Total 23 (delta 14), reused 0 (delta 0)
> [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 12803
> --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12803, si_uid=1000, si_status=0, si_utime=2, si_stime=6} ---
> read(3,

If FD 6 were wired up to something in the child and the child exited
(which, having received SIGCHLD, is a safe bet), then we'd expect this
to see this process get EOF.

It's not clear to me what's going on here, but I think this code is
ending up in connect.c (search for "transport/file").  Maybe someone
else has an idea?
-- 
brian m. carlson (he/him or they/them)
Toronto, Ontario, CA

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Re: git push locks up forever, file protocol

[Jeff Hostetler]

On 4/21/22 9:31 PM, brian m. carlson wrote:
> On 2022-04-21 at 08:30:50, Jason Morgan wrote:
>> Hi,
>>
>> We have a remote repo accessed using the 'file:' protocol, mounted over Samba using drvfs into a WSL2 instance of Ubuntu 20.04.
>>
>> We find a 'git push' waits forever. git version 2.25.1
> 
> I seem to recall that we've fixed some various issues with protocol
> handling in the 2.29 timeframe.  Is it possible you could try 2.36.0 to
> see if you can reproduce it there?
> 
> Also, it would be interesting to see if there's a difference in
> behaviour between setting protocol.version to 0 and setting it to 2.
> That might tell us something that would help tracking this down.
> 
>> Over a local LAN this works fine, but over a VPN this fails, hinting at some sort of race condition.
>>
>> Output from strace hints that git is trying (and failing) to read from a closed file handle.
> 
> I don't think this is the case.  If Git were trying to read from a
> closed file handle, the kernel would immediately return -1 with errno
> set to EBADF.  Those operations won't block because there's nothing to
> read.
> 
>> Final output from strace:
>>
>> -----------
>> openat(AT_FDCWD, ".git/objects/ad/065dad4384ae8c81c120c562985078d1f7b34b", O_RDONLY|O_CLOEXEC) = 3
>> fstat(3, {st_mode=S_IFREG|0444, st_size=152, ...}) = 0
>> mmap(NULL, 152, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
>> close(3)                                = 0
>> munmap(0x7f3e0e4af000, 152)             = 0
>> openat(AT_FDCWD, ".git/objects/30/2508dfe5201db6c000ebf17b0c69e3afb31218", O_RDONLY|O_CLOEXEC) = 3
>> fstat(3, {st_mode=S_IFREG|0555, st_size=214, ...}) = 0
>> mmap(NULL, 214, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
>> close(3)                                = 0
>> munmap(0x7f3e0e4af000, 214)             = 0
>> openat(AT_FDCWD, ".git/objects/d2/2323ec2ec40a74fbd519509662254c3cfda206", O_RDONLY|O_CLOEXEC) = 3
>> fstat(3, {st_mode=S_IFREG|0444, st_size=161, ...}) = 0
>> mmap(NULL, 161, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
>> close(3)                                = 0
> 
> FD 3 is closed here...
> 
>> munmap(0x7f3e0e4af000, 161)             = 0
>> access(".git/hooks/pre-push", X_OK)     = -1 ENOENT (No such file or directory)
>> write(4, "00953ea50e3c1f49c33f7dbbb5e3a310"..., 149) = 149
>> write(4, "0000", 4)                     = 4
>> pipe([3, 6])                            = 0
> 
> And then it's recreated here as one part of a pipe, so it isn't closed.
> 
>> fcntl(6, F_GETFD)                       = 0
>> fcntl(6, F_SETFD, FD_CLOEXEC)           = 0
>> mmap(NULL, 8392704, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7f3e0d641000
>> mprotect(0x7f3e0d642000, 8388608, PROT_READ|PROT_WRITE) = 0
>> clone(child_stack=0x7f3e0de40fb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tid=[12802], tls=0x7f3e0de41700, child_tidptr=0x7f3e0de419d0) = 12802
> 
> My guess is that in the child (which isn't shown here) that FD 6 is
> hooked up to either standard output or standard error.  You'd need to
> follow children to see.
> 
>> pipe([7, 8])                            = 0
>> stat("/usr/lib/git-core/git", {st_mode=S_IFREG|0755, st_size=3093072, ...}) = 0
>> pipe([9, 10])                           = 0
>> rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
>> clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f3e0e1dae50) = 12803
>> rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
>> close(10)                               = 0
>> read(9, "", 8)                          = 0
>> close(9)                                = 0
>> close(7)                                = 0
>> close(4)                                = 0
>> fcntl(8, F_GETFL)                       = 0x1 (flags O_WRONLY)
>> openat(AT_FDCWD, ".git/objects/3e", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 4
>> fstat(4, {st_mode=S_IFDIR|0777, st_size=4096, ...}) = 0
>> getdents64(4, /* 22 entries */, 32768)  = 1328
>> getdents64(4, /* 0 entries */, 32768)   = 0
>> close(4)                                = 0
>> fstat(8, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
>> write(8, "^3ea50e3c1f49c33f7dbbb5e3a31017f"..., 83) = 83
>> close(8)                                = 0
>> Enumerating objects: 31, done.ts: 1
>> Counting objects: 100% (31/31), done.
>> Delta compression using up to 8 threads
>> Compressing objects: 100% (23/23), done.
>> Writing objects: 100% (23/23), 5.60 KiB | 212.00 KiB/s, done.
>> Total 23 (delta 14), reused 0 (delta 0)
>> [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 12803
>> --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12803, si_uid=1000, si_status=0, si_utime=2, si_stime=6} ---
>> read(3,
> 
> If FD 6 were wired up to something in the child and the child exited
> (which, having received SIGCHLD, is a safe bet), then we'd expect this
> to see this process get EOF.
> 
> It's not clear to me what's going on here, but I think this code is
> ending up in connect.c (search for "transport/file").  Maybe someone
> else has an idea?
> 

Not sure I can add anything here to what Brian has already said,
but you might try setting GIT_TRACE2_PERF to an absolute path of
a file or an existing directory.  That'll give you tracing around
the child.

Jeff

RE: git push locks up forever, file protocol

[rsbecker]

On April 22, 2022 10:17 AM, Jeff Hostetler wrote:
>On 4/21/22 9:31 PM, brian m. carlson wrote:
>> On 2022-04-21 at 08:30:50, Jason Morgan wrote:
>>> Hi,
>>>
>>> We have a remote repo accessed using the 'file:' protocol, mounted over
>Samba using drvfs into a WSL2 instance of Ubuntu 20.04.
>>>
>>> We find a 'git push' waits forever. git version 2.25.1
>>
>> I seem to recall that we've fixed some various issues with protocol
>> handling in the 2.29 timeframe.  Is it possible you could try 2.36.0
>> to see if you can reproduce it there?
>>
>> Also, it would be interesting to see if there's a difference in
>> behaviour between setting protocol.version to 0 and setting it to 2.
>> That might tell us something that would help tracking this down.
>>
>>> Over a local LAN this works fine, but over a VPN this fails, hinting at some sort
>of race condition.
>>>
>>> Output from strace hints that git is trying (and failing) to read from a closed file
>handle.
>>
>> I don't think this is the case.  If Git were trying to read from a
>> closed file handle, the kernel would immediately return -1 with errno
>> set to EBADF.  Those operations won't block because there's nothing to
>> read.
>>
>>> Final output from strace:
>>>
>>> -----------
>>> openat(AT_FDCWD,
>>> ".git/objects/ad/065dad4384ae8c81c120c562985078d1f7b34b",
>>> O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0444, st_size=152,
>>> ...}) = 0 mmap(NULL, 152, PROT_READ, MAP_PRIVATE, 3, 0) =
>>> 0x7f3e0e4af000
>>> close(3)                                = 0 munmap(0x7f3e0e4af000,
>>> 152)             = 0 openat(AT_FDCWD,
>>> ".git/objects/30/2508dfe5201db6c000ebf17b0c69e3afb31218",
>>> O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0555, st_size=214,
>>> ...}) = 0 mmap(NULL, 214, PROT_READ, MAP_PRIVATE, 3, 0) =
>>> 0x7f3e0e4af000
>>> close(3)                                = 0 munmap(0x7f3e0e4af000,
>>> 214)             = 0 openat(AT_FDCWD,
>>> ".git/objects/d2/2323ec2ec40a74fbd519509662254c3cfda206",
>>> O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0444, st_size=161,
>>> ...}) = 0 mmap(NULL, 161, PROT_READ, MAP_PRIVATE, 3, 0) =
>>> 0x7f3e0e4af000
>>> close(3)                                = 0
>>
>> FD 3 is closed here...
>>
>>> munmap(0x7f3e0e4af000, 161)             = 0
>>> access(".git/hooks/pre-push", X_OK)     = -1 ENOENT (No such file or
>>> directory) write(4, "00953ea50e3c1f49c33f7dbbb5e3a310"..., 149) = 149
>>> write(4, "0000", 4)                     = 4 pipe([3, 6])
>>> = 0
>>
>> And then it's recreated here as one part of a pipe, so it isn't closed.
>>
>>> fcntl(6, F_GETFD)                       = 0 fcntl(6, F_SETFD,
>>> FD_CLOEXEC)           = 0 mmap(NULL, 8392704, PROT_NONE,
>>> MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7f3e0d641000
>>> mprotect(0x7f3e0d642000, 8388608, PROT_READ|PROT_WRITE) = 0
>>> clone(child_stack=0x7f3e0de40fb0,
>>>
>flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|C
>LONE_
>>> SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
>>> parent_tid=[12802], tls=0x7f3e0de41700, child_tidptr=0x7f3e0de419d0)
>>> = 12802
>>
>> My guess is that in the child (which isn't shown here) that FD 6 is
>> hooked up to either standard output or standard error.  You'd need to
>> follow children to see.
>>
>>> pipe([7, 8])                            = 0
>>> stat("/usr/lib/git-core/git", {st_mode=S_IFREG|0755, st_size=3093072,
>>> ...}) = 0 pipe([9, 10])                           = 0
>>> rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0
>>> clone(child_stack=NULL,
>>> flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
>>> child_tidptr=0x7f3e0e1dae50) = 12803 rt_sigprocmask(SIG_SETMASK, [],
>>> NULL, 8) = 0
>>> close(10)                               = 0 read(9, "", 8)
>>> = 0
>>> close(9)                                = 0
>>> close(7)                                = 0
>>> close(4)                                = 0 fcntl(8, F_GETFL)
>>> = 0x1 (flags O_WRONLY) openat(AT_FDCWD, ".git/objects/3e",
>>> O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 4 fstat(4,
>>> {st_mode=S_IFDIR|0777, st_size=4096, ...}) = 0 getdents64(4, /* 22
>>> entries */, 32768)  = 1328 getdents64(4, /* 0 entries */, 32768)   =
>>> 0
>>> close(4)                                = 0 fstat(8,
>>> {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0 write(8,
>>> "^3ea50e3c1f49c33f7dbbb5e3a31017f"..., 83) = 83
>>> close(8)                                = 0 Enumerating objects: 31,
>>> done.ts: 1 Counting objects: 100% (31/31), done.
>>> Delta compression using up to 8 threads Compressing objects: 100%
>>> (23/23), done.
>>> Writing objects: 100% (23/23), 5.60 KiB | 212.00 KiB/s, done.
>>> Total 23 (delta 14), reused 0 (delta 0)
>>> [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 12803
>>> --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12803,
>>> si_uid=1000, si_status=0, si_utime=2, si_stime=6} --- read(3,
>>
>> If FD 6 were wired up to something in the child and the child exited
>> (which, having received SIGCHLD, is a safe bet), then we'd expect this
>> to see this process get EOF.
>>
>> It's not clear to me what's going on here, but I think this code is
>> ending up in connect.c (search for "transport/file").  Maybe someone
>> else has an idea?
>>
>
>Not sure I can add anything here to what Brian has already said, but you might try
>setting GIT_TRACE2_PERF to an absolute path of a file or an existing directory.
>That'll give you tracing around the child.

The only time I've seen something like this was when we had a poll issue setting a continuation after a non-block condition with no data that caused the stack to get confused. IIRC it was about 4 years ago and one of my first contributions. I don't think this is the same thing because poll does not seem to be involved.
--Randall

RE: git push locks up forever, file protocol

[Jason Morgan]

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Brian/Jeff

As requested....

I tried git 2.25.1 (stock Ubuntu 20.04) and git 2.36.0 (from ppa:git-core/ppa)

I tried both file://<mount_point> and /<mount_point> for remote

I tried both git -c protocol.version=0 as well as git -c protocol.version=2

All with exactly the same symptoms, halts at read(3,...

I also tried a user bindfs mount instead of a mount bind in fstab as I noticed that I could not access the mount point from the latter over \\wsl$ in windows but I could with bindfs.
The change made no difference to git

Trace GIT_TRACE2_PERF files attached for "git push" on v2.36.0 with /<mount_point> protocol (files 20220422T150*)
Last few lines of strace for each combination also attached.
Repeated for "git push" using the file:// protocol  (files 20220422T1555*)

I provided the 'default' GIT_TRACE2_PERF invocation (rather than strace and/or -c) as I thought that it would better represent normal program flow.

Hope that hints at the issue.
Let me know if there is anything else I can try.


On 4/21/22 9:31 PM, brian m. carlson wrote:
> On 2022-04-21 at 08:30:50, Jason Morgan wrote:
>> Hi,
>>
>> We have a remote repo accessed using the 'file:' protocol, mounted over Samba using drvfs into a WSL2 instance of Ubuntu 20.04.
>>
>> We find a 'git push' waits forever. git version 2.25.1
>
> I seem to recall that we've fixed some various issues with protocol 
> handling in the 2.29 timeframe.  Is it possible you could try 2.36.0 
> to see if you can reproduce it there?
>
> Also, it would be interesting to see if there's a difference in 
> behaviour between setting protocol.version to 0 and setting it to 2.
> That might tell us something that would help tracking this down.
>
>> Over a local LAN this works fine, but over a VPN this fails, hinting at some sort of race condition.
>>
>> Output from strace hints that git is trying (and failing) to read from a closed file handle.
>
> I don't think this is the case.  If Git were trying to read from a 
> closed file handle, the kernel would immediately return -1 with errno 
> set to EBADF.  Those operations won't block because there's nothing to 
> read.
>
>> Final output from strace:
>>
>> -----------
>> openat(AT_FDCWD, 
>> ".git/objects/ad/065dad4384ae8c81c120c562985078d1f7b34b", 
>> O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0444, st_size=152, ...}) = 0 mmap(NULL, 152, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
>> close(3)                                = 0
>> munmap(0x7f3e0e4af000, 152)             = 0
>> openat(AT_FDCWD, 
>> ".git/objects/30/2508dfe5201db6c000ebf17b0c69e3afb31218", 
>> O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0555, st_size=214, ...}) = 0 mmap(NULL, 214, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
>> close(3)                                = 0
>> munmap(0x7f3e0e4af000, 214)             = 0
>> openat(AT_FDCWD, 
>> ".git/objects/d2/2323ec2ec40a74fbd519509662254c3cfda206", 
>> O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0444, st_size=161, ...}) = 0 mmap(NULL, 161, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f3e0e4af000
>> close(3)                                = 0
>
> FD 3 is closed here...
>
>> munmap(0x7f3e0e4af000, 161)             = 0
>> access(".git/hooks/pre-push", X_OK)     = -1 ENOENT (No such file or directory)
>> write(4, "00953ea50e3c1f49c33f7dbbb5e3a310"..., 149) = 149
>> write(4, "0000", 4)                     = 4
>> pipe([3, 6])                            = 0
>
> And then it's recreated here as one part of a pipe, so it isn't closed.
>
>> fcntl(6, F_GETFD)                       = 0
>> fcntl(6, F_SETFD, FD_CLOEXEC)           = 0
>> mmap(NULL, 8392704, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, 
>> -1, 0) = 0x7f3e0d641000 mprotect(0x7f3e0d642000, 8388608, 
>> PROT_READ|PROT_WRITE) = 0 clone(child_stack=0x7f3e0de40fb0, 
>> flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_
>> SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, 
>> parent_tid=[12802], tls=0x7f3e0de41700, child_tidptr=0x7f3e0de419d0) 
>> = 12802
>
> My guess is that in the child (which isn't shown here) that FD 6 is 
> hooked up to either standard output or standard error.  You'd need to 
> follow children to see.
>
>> pipe([7, 8])                            = 0
>> stat("/usr/lib/git-core/git", {st_mode=S_IFREG|0755, st_size=3093072, ...}) = 0
>> pipe([9, 10])                           = 0
>> rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [], 8) = 0 
>> clone(child_stack=NULL, 
>> flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7f3e0e1dae50) = 12803 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
>> close(10)                               = 0
>> read(9, "", 8)                          = 0
>> close(9)                                = 0
>> close(7)                                = 0
>> close(4)                                = 0
>> fcntl(8, F_GETFL)                       = 0x1 (flags O_WRONLY)
>> openat(AT_FDCWD, ".git/objects/3e", 
>> O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 4 fstat(4, 
>> {st_mode=S_IFDIR|0777, st_size=4096, ...}) = 0 getdents64(4, /* 22 entries */, 32768)  = 1328
>> getdents64(4, /* 0 entries */, 32768)   = 0
>> close(4)                                = 0
>> fstat(8, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0 write(8, 
>> "^3ea50e3c1f49c33f7dbbb5e3a31017f"..., 83) = 83
>> close(8)                                = 0
>> Enumerating objects: 31, done.ts: 1
>> Counting objects: 100% (31/31), done.
>> Delta compression using up to 8 threads Compressing objects: 100% 
>> (23/23), done.
>> Writing objects: 100% (23/23), 5.60 KiB | 212.00 KiB/s, done.
>> Total 23 (delta 14), reused 0 (delta 0)
>> [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 12803
>> --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=12803, 
>> si_uid=1000, si_status=0, si_utime=2, si_stime=6} --- read(3,
>
> If FD 6 were wired up to something in the child and the child exited 
> (which, having received SIGCHLD, is a safe bet), then we'd expect this 
> to see this process get EOF.
>
> It's not clear to me what's going on here, but I think this code is 
> ending up in connect.c (search for "transport/file").  Maybe someone 
> else has an idea?
>

Not sure I can add anything here to what Brian has already said, but you might try setting GIT_TRACE2_PERF to an absolute path of a file or an existing directory.  That'll give you tracing around the child.

Jeff


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