Commit 4121b433 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by David Howells
Browse files

afs: fix the usage of read_seqbegin_or_lock() in afs_lookup_volume_rcu() 



David Howells says:

 (2) afs_lookup_volume_rcu().

     There can be a lot of volumes known by a system.  A thousand would
     require a 10-step walk and this is drivable by remote operation, so I
     think this should probably take a lock on the second pass too.

Make the "seq" counter odd on the 2nd pass, otherwise read_seqbegin_or_lock()
never takes the lock.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/20231130115606.GA21571@redhat.com/
parent 2daa6404

fs/afs/callback.c

+2 −1
Original line number Diff line number Diff line
@@ -110,13 +110,14 @@ static struct afs_volume *afs_lookup_volume_rcu(struct afs_cell *cell, 
{

	struct afs_volume *volume = NULL;

	struct rb_node *p;

	int seq = 0;

	int seq = 1;



	do {

		/* Unfortunately, rbtree walking doesn't give reliable results

		 * under just the RCU read lock, so we have to check for

		 * changes.

		 */

		seq++; /* 2 on the 1st/lockless path, otherwise odd */

		read_seqbegin_or_lock(&cell->volume_lock, &seq);



		p = rcu_dereference_raw(cell->volumes.rb_node);