From 53113dc8254cae9a27e321e539d2d876677e61b9 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>

Date: Fri, 7 Jun 2013 22:01:03 -0400

Subject: [PATCH] journal: letting (interleaved) seqnums go

In the following scenario:

  server creates system.journal

  server creates user-1000.journal

both journals share the same seqnum_id.

Then

  server writes to user-1000.journal first,

  and server writes to system.journal a bit later,

and everything is fine.

The server then terminates (crash, reboot, rsyslog testing,

whatever), and user-1000.journal has entries which end with

a lower seqnum than system.journal. Now

  server is restarted

  server opens user-1000.journal and writes entries to it...

BAM! duplicate seqnums for the same seqnum_id.

Now, we usually don't see that happen, because system.journal

is closed last, and opened first. Since usually at least one

message is written during boot and lands in the system.journal,

the seqnum is initialized from it, and is set to a number higher

than than anything found in user journals. Nevertheless, if

system.journal is corrupted and is rotated, it can happen that

an entry is written to the user journal with a seqnum that is

a duplicate with an entry found in the corrupted system.journal~.

When browsing the journal, journalctl can fall into a loop

where it tries to follow the seqnums, and tries to go the

next location by seqnum, and is transported back in time to

to the older duplicate seqnum. There is not way to find

out the maximum seqnum used in a multiple files, without

actually looking at all of them. But we don't want to do

that because it would be slow, and actually it isn't really

possible, because a file might e.g. be temporarily unaccessible.

Fix the problem by using different seqnum series for user

journals. Using the same seqnum series for rotated journals

is still fine, because we know that nothing will write

to the rotated journal anymore.

Likely related:

https://bugs.freedesktop.org/show_bug.cgi?id=64566

https://bugs.freedesktop.org/show_bug.cgi?id=59856

https://bugs.freedesktop.org/show_bug.cgi?id=64296

https://bugs.archlinux.org/task/35581

https://bugzilla.novell.com/show_bug.cgi?id=817778

Possibly related:

https://bugs.freedesktop.org/show_bug.cgi?id=64293

Conflicts:

	src/journal/journald-server.c

---

 src/journal/journald-server.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c

index cc52b8a..cde63c8 100644

--- a/src/journal/journald-server.c

+++ b/src/journal/journald-server.c

@@ -280,7 +280,7 @@ static JournalFile* find_journal(Server *s, uid_t uid) {

                 journal_file_close(f);

         }

-        r = journal_file_open_reliably(p, O_RDWR|O_CREAT, 0640, s->compress, s->seal, &s->system_metrics, s->mmap, s->system_journal, &f);

+        r = journal_file_open_reliably(p, O_RDWR|O_CREAT, 0640, s->compress, s->seal, &s->system_metrics, s->mmap, NULL, &f);

         free(p);

         if (r < 0)

-- 

1.8.2.1