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Commit 4a1360d0 authored by Aurelien Aptel's avatar Aurelien Aptel Committed by Steve French
Browse files

CIFS: document tcon/ses/server refcount dance 



Signed-off-by: default avatarAurelien Aptel <aaptel@suse.com>
Signed-off-by: default avatarSteve French <smfrench@gmail.com>
Reviewed-by: default avatarRonnie Sahlberg <lsahlber@redhat.com>
parent 6b314714

fs/cifs/connect.c

+31 −1
Original line number Diff line number Diff line
@@ -2704,6 +2704,13 @@ cifs_set_cifscreds(struct smb_vol *vol __attribute__((unused)), 
}

#endif /* CONFIG_KEYS */



/**

 * cifs_get_smb_ses - get a session matching @volume_info data from @server

 *

 * This function assumes it is being called from cifs_mount() where we

 * already got a server reference (server refcount +1). See

 * cifs_get_tcon() for refcount explanations.

 */

static struct cifs_ses *

cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb_vol *volume_info)

{
@@ -2877,6 +2884,26 @@ cifs_put_tcon(struct cifs_tcon *tcon) 
	cifs_put_smb_ses(ses);

}



/**

 * cifs_get_tcon - get a tcon matching @volume_info data from @ses

 *

 * - tcon refcount is the number of mount points using the tcon.

 * - ses refcount is the number of tcon using the session.

 *

 * 1. This function assumes it is being called from cifs_mount() where

 *    we already got a session reference (ses refcount +1).

 *

 * 2. Since we're in the context of adding a mount point, the end

 *    result should be either:

 *

 * a) a new tcon already allocated with refcount=1 (1 mount point) and

 *    its session refcount incremented (1 new tcon). This +1 was

 *    already done in (1).

 *

 * b) an existing tcon with refcount+1 (add a mount point to it) and

 *    identical ses refcount (no new tcon). Because of (1) we need to

 *    decrement the ses refcount.

 */

static struct cifs_tcon *

cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)

{
@@ -2885,8 +2912,11 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info) 


	tcon = cifs_find_tcon(ses, volume_info);

	if (tcon) {

		/*

		 * tcon has refcount already incremented but we need to

		 * decrement extra ses reference gotten by caller (case b)

		 */

		cifs_dbg(FYI, "Found match on UNC path\n");

		/* existing tcon already has a reference */

		cifs_put_smb_ses(ses);

		return tcon;

	}