Prevent deadlock between open_shroot() and cifs_mark_open_files_invalid() by releasing the lock before entering SMB2_open, taking it again after and checking if we still need to use the result. Link: https://lore.kernel.org/linux-cifs/684ed01c-cbca-2716-bc28-b0a59a0f8521@xxxxxxxxxxxxxxxxxxxxxxxxx/T/#u Fixes: 3d4ef9a15343 ("smb3: fix redundant opens on root") Signed-off-by: Aurelien Aptel <aaptel@xxxxxxxx> --- Changes since v1: * added SMB2_close() of extra root handle * copied valid handle to caller's pfid * added reference get() of the handle Please review carefuly, I haven't tested this. fs/cifs/smb2ops.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c index aa71e620f3cd..53e14fd74abc 100644 --- a/fs/cifs/smb2ops.c +++ b/fs/cifs/smb2ops.c @@ -609,7 +609,49 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid) oparams.fid = pfid; oparams.reconnect = false; + /* + * We do not hold the lock for the open because in case + * SMB2_open needs to reconnect, it will end up calling + * cifs_mark_open_files_invalid() which takes the lock again + * thus causing a deadlock + */ + mutex_unlock(&tcon->crfid.fid_mutex); rc = SMB2_open(xid, &oparams, &srch_path, &oplock, NULL, NULL, NULL); + mutex_lock(&tcon->crfid.fid_mutex); + + /* + * Now we need to check again as the cached root might have + * been successfully re-opened from a concurrent process + */ + + if (tcon->crfid.is_valid) { + /* work was already done */ + + /* stash fids for close() later */ + struct cifs_fid fid = { + .persistent_fid = pfid->persistent_fid, + .volatile_fid = pfid->volatile_fid, + }; + + /* + * caller expects this func to set pfid to a valid + * cached root, so we copy the existing one and get a + * reference. + */ + memcpy(pfid, tcon->crfid.fid, sizeof(*pfid)); + kref_get(&tcon->crfid.refcount); + + mutex_unlock(&tcon->crfid.fid_mutex); + + if (rc == 0) { + /* close extra handle outside of crit sec */ + SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid); + } + return 0; + } + + /* Cached root is still invalid, continue normaly */ + if (rc == 0) { memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid)); tcon->crfid.tcon = tcon; @@ -617,6 +659,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid) kref_init(&tcon->crfid.refcount); kref_get(&tcon->crfid.refcount); } + mutex_unlock(&tcon->crfid.fid_mutex); return rc; } -- 2.16.4
