[PATCH 0/3] git-svn: fixes for intermittent SIGPIPE

[PATCH 0/3] git-svn: fixes for intermittent SIGPIPE

[Roman Kagan]

In my work environment subversion is still being used as the main
revision control system.  Therefore many people who prefer to work with
git have to resort to git-svn.

However, in many configurations it used to suffer from the notorious
"git-svn died of signal 13" problem (see e.g.
http://thread.gmane.org/gmane.comp.version-control.git/134936 and the
links therein).

I believe to have tracked down the issue to the connection being closed
by the server when http keep-alive is in use, and the client dying on
SIGPIPE because its handler is left at SIG_DFL when a new request is
being made.

The patches have been tested on

- Linux Fedora 16 x86_64, git 1.7.7.6, perl v5.14.2, svn 1.6.17
- Windows 7 x64 + Cygwin, git 1.7.9, perl v5.10.1, svn 1.7.4,
- Windows 7 x64 + MsysGit, git 1.7.9.msysgit.0, perl v5.8.8, svn 1.4.6

This is the third version of the series; compared to the previous submission
the log message of the first patch was reworded to make it more palatable.

Roman Kagan (3):
  git-svn: use POSIX::sigprocmask to block signals
  git-svn: ignore SIGPIPE
  git-svn: drop redundant blocking of SIGPIPE

 git-svn.perl |   20 ++++++++++++++------
 1 files changed, 14 insertions(+), 6 deletions(-)

-- 
1.7.7.6

[PATCH 1/3] git-svn: use POSIX::sigprocmask to block signals

[Roman Kagan]

In order to maintain consistency of the database mapping svn revision
numbers to git commit ids, rev_map_set() defers signal processing until
it's finished with an append transaction.[*]

The conventional way to achieve this is through sigprocmask(), which is
available in perl in the standard POSIX module.

This is implemented by this patch.  One important consequence of it is
that the signal handlers won't be unconditionally set to SIG_DFL anymore
upon the first invocation of rev_map_set() as they used to.  As a
result, the signals ignored by git-svn parent will remain ignored;
otherwise the behavior remains the same.

This patch paves the way to ignoring SIGPIPE throughout git-svn which
will be done in the followup patch.

[*] Deferring signals is not enough to ensure the database consistency:
the program may die on SIGKILL or power loss, run out of disk space,
etc.  However that's a separate issue that this patch doesn't address.

Signed-off-by: Roman Kagan <rkagan@mail.ru>
---
 git-svn.perl |   15 +++++++++------
 1 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/git-svn.perl b/git-svn.perl
index 4334b95..570504c 100755
--- a/git-svn.perl
+++ b/git-svn.perl
@@ -2031,6 +2031,7 @@ use IPC::Open3;
 use Time::Local;
 use Memoize;  # core since 5.8.0, Jul 2002
 use Memoize::Storable;
+use POSIX qw(:signal_h);
 
 my ($_gc_nr, $_gc_period);
 
@@ -4059,11 +4060,14 @@ sub rev_map_set {
 	length $commit == 40 or die "arg3 must be a full SHA1 hexsum\n";
 	my $db = $self->map_path($uuid);
 	my $db_lock = "$db.lock";
-	my $sig;
+	my $sigmask;
 	$update_ref ||= 0;
 	if ($update_ref) {
-		$SIG{INT} = $SIG{HUP} = $SIG{TERM} = $SIG{ALRM} = $SIG{PIPE} =
-		            $SIG{USR1} = $SIG{USR2} = sub { $sig = $_[0] };
+		$sigmask = POSIX::SigSet->new();
+		my $signew = POSIX::SigSet->new(SIGINT, SIGHUP, SIGTERM,
+			SIGALRM, SIGPIPE, SIGUSR1, SIGUSR2);
+		sigprocmask(SIG_BLOCK, $signew, $sigmask) or
+			croak "Can't block signals: $!";
 	}
 	mkfile($db);
 
@@ -4102,9 +4106,8 @@ sub rev_map_set {
 	                            "$db_lock => $db ($!)\n";
 	delete $LOCKFILES{$db_lock};
 	if ($update_ref) {
-		$SIG{INT} = $SIG{HUP} = $SIG{TERM} = $SIG{ALRM} = $SIG{PIPE} =
-		            $SIG{USR1} = $SIG{USR2} = 'DEFAULT';
-		kill $sig, $$ if defined $sig;
+		sigprocmask(SIG_SETMASK, $sigmask) or
+			croak "Can't restore signal mask: $!";
 	}
 }
 
-- 
1.7.7.6

[PATCH 2/3] git-svn: ignore SIGPIPE

[Roman Kagan]

In HTTP with keep-alive it's not uncommon for the client to notice that
the server decided to stop maintaining the current connection only when
sending a new request.  This naturally results in -EPIPE and possibly
SIGPIPE.

The subversion library itself makes no provision for SIGPIPE.  Some
combinations of the underlying libraries do (typically SIG_IGN-ing it),
some don't.

Presumably for that reason all subversion commands set SIGPIPE to
SIG_IGN early in their main()-s.

So should we.

This, together with the previous patch, fixes the notorious "git-svn
died of signal 13" problem (see e.g.
http://thread.gmane.org/gmane.comp.version-control.git/134936).

Signed-off-by: Roman Kagan <rkagan@mail.ru>
---
 git-svn.perl |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/git-svn.perl b/git-svn.perl
index 570504c..aa14564 100755
--- a/git-svn.perl
+++ b/git-svn.perl
@@ -36,6 +36,11 @@ $ENV{TZ} = 'UTC';
 $| = 1; # unbuffer STDOUT
 
 sub fatal (@) { print STDERR "@_\n"; exit 1 }
+
+# All SVN commands do it.  Otherwise we may die on SIGPIPE when the remote
+# repository decides to close the connection which we expect to be kept alive.
+$SIG{PIPE} = 'IGNORE';
+
 sub _req_svn {
 	require SVN::Core; # use()-ing this causes segfaults for me... *shrug*
 	require SVN::Ra;
-- 
1.7.7.6

[PATCH 3/3] git-svn: drop redundant blocking of SIGPIPE

[Roman Kagan]

Now that SIGPIPE is ignored there's no point blocking it.

Signed-off-by: Roman Kagan <rkagan@mail.ru>
---
 git-svn.perl |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/git-svn.perl b/git-svn.perl
index aa14564..f8e9ef0 100755
--- a/git-svn.perl
+++ b/git-svn.perl
@@ -4070,7 +4070,7 @@ sub rev_map_set {
 	if ($update_ref) {
 		$sigmask = POSIX::SigSet->new();
 		my $signew = POSIX::SigSet->new(SIGINT, SIGHUP, SIGTERM,
-			SIGALRM, SIGPIPE, SIGUSR1, SIGUSR2);
+			SIGALRM, SIGUSR1, SIGUSR2);
 		sigprocmask(SIG_BLOCK, $signew, $sigmask) or
 			croak "Can't block signals: $!";
 	}
-- 
1.7.7.6

Re: [PATCH 0/3] git-svn: fixes for intermittent SIGPIPE

[Eric Wong]

Roman Kagan <rkagan@mail.ru> wrote:
> This is the third version of the series; compared to the previous submission
> the log message of the first patch was reworded to make it more palatable.
> 
> Roman Kagan (3):
>   git-svn: use POSIX::sigprocmask to block signals
>   git-svn: ignore SIGPIPE
>   git-svn: drop redundant blocking of SIGPIPE

Thanks for this series, acked and pushed to git://bogomips.org/git-svn

Re: [PATCH 0/3] git-svn: fixes for intermittent SIGPIPE

[Junio C Hamano]

Eric Wong <normalperson@yhbt.net> writes:

> Roman Kagan <rkagan@mail.ru> wrote:
>> This is the third version of the series; compared to the previous submission
>> the log message of the first patch was reworded to make it more palatable.
>> 
>> Roman Kagan (3):
>>   git-svn: use POSIX::sigprocmask to block signals
>>   git-svn: ignore SIGPIPE
>>   git-svn: drop redundant blocking of SIGPIPE
>
> Thanks for this series, acked and pushed to git://bogomips.org/git-svn

Thanks, both. I agree that the first one is much more nicely explained
than the previous one.

[PATCH 0/3] git-svn: fixes for intermittent SIGPIPE

[Roman Kagan]

In my work environment subversion is still being used as the main
revision control system.  Therefore many people who prefer to work with
git have to resort to git-svn.

However, in many configurations it used to suffer from the notorious
"git-svn died of signal 13" problem (see e.g.
http://thread.gmane.org/gmane.comp.version-control.git/134936 and the
links therein).

I believe to have tracked down the issue to the connection being closed
by the server when http keep-alive is in use, and the client dying on
SIGPIPE because its handler is left at SIG_DFL when a new request is
being made.

The patches have been tested on

- Linux Fedora 16 x86_64, git 1.7.7.6, perl v5.14.2, svn 1.6.17
- Windows 7 x64 + Cygwin, git 1.7.9, perl v5.10.1, svn 1.7.4,
- Windows 7 x64 + MsysGit, git 1.7.9.msysgit.0, perl v5.8.8, svn 1.4.6

This is the second version of the series; it only differs from the first
submission in that it includes the third patch with a cosmetic cleanup.

Roman Kagan (3):
  git-svn: use POSIX::sigprocmask to block signals
  git-svn: ignore SIGPIPE
  git-svn: drop redundant blocking of SIGPIPE

 git-svn.perl |   20 ++++++++++++++------
 1 files changed, 14 insertions(+), 6 deletions(-)

-- 
1.7.7.6