Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

bcache: avoid journal no-space deadlock by reserving 1 journal bucket

The journal no-space deadlock was reported time to time. Such deadlock can happen in the following situation.

When all journal buckets are fully filled by active jset with heavy write I/O load, the cache set registration (after a reboot) will load all active jsets and inserting them into the btree again (which is called journal replay). If a journaled bkey is inserted into a btree node and results btree node split, new journal request might be triggered. For example, the btree grows one more level after the node split, then the root node record in cache device super block will be upgrade by bch_journal_meta() from bch_btree_set_root(). But there is no space in journal buckets, the journal replay has to wait for new journal bucket to be reclaimed after at least one journal bucket replayed. This is one example that how the journal no-space deadlock happens.

The solution to avoid the deadlock is to reserve 1 journal bucket in run time, and only permit the reserved journal bucket to be used during cache set registration procedure for things like journal replay. Then the journal space will never be fully filled, there is no chance for journal no-space deadlock to happen anymore.

This patch adds a new member "bool do_reserve" in struct journal, it is inititalized to 0 (false) when struct journal is allocated, and set to 1 (true) by bch_jour…