[PATCH stable request 3.10] vfs: Remove incorrect debugging WARN in prepend_path

[PATCH stable request 3.10] vfs: Remove incorrect debugging WARN in prepend_path

[Vinson Lee]

From: Vinson Lee <vlee@twitter.com>

Hi.

Please backport upstream 4.2 commit 93e3bce6287e1fb3e60d3324ed08555b5bbafa89
("vfs: Remove incorrect debugging WARN in prepend_path") to stable kernel 3.10.

This patch has already been backported to stable kernels 3.12, 3.13, 3.14,
3.16, 3.18, 4.0, and 4.1.

The upstream patch does not apply cleanly and a backport is provided.

This patch fixes 3.13 commit f48cfddc6729e
("vfs: In d_path don't call d_dname on a mount point"), but this patch was
itself was backported in 3.10.28.

This patch addresses this warning seen in 3.10.76.

------------[ cut here ]------------
WARNING: at fs/dcache.c:2576 prepend_path+0x12b/0x17c()
Root dentry has weird name <>
Modules linked in: sch_fq_codel sch_htb cls_basic act_mirred cls_u32 veth sch_ingress netconsole configfs ipv6 dm_multipath scsi_dh video sbs sbshc hed acpi_pad a
 parport_pc lp parport tcp_diag inet_diag ipmi_si ipmi_devintf ipmi_msghandler dell_rbu sg iTCO_wdt iTCO_vendor_support dcdbas igb i2c_algo_bit ptp pps_core i7cor
ioatdma i2c_i801 shpchp i2c_core lpc_ich microcode dca mfd_core freq_table mperf ahci libahci libata sd_mod scsi_mod
CPU: 9 PID: 13242 Comm: lsof Tainted: G      D W    3.10.76 #1
 0000000000000000 ffff880b28ef3da0 ffffffff8146857f ffff880b28ef3dd8
 ffffffff8103cc01 ffff880b28ef3de8 ffff88060275fa20 ffff8803d4dbb740
 ffff88060275fa00 0000000000000000 ffff880b28ef3e38 ffffffff8103cc65
Call Trace:
 [<ffffffff8146857f>] dump_stack+0x19/0x1b
 [<ffffffff8103cc01>] warn_slowpath_common+0x65/0x7d
 [<ffffffff8103cc65>] warn_slowpath_fmt+0x4c/0x4e
 [<ffffffff8113dd5b>] prepend_path+0x12b/0x17c
 [<ffffffff8113de85>] d_path+0xd9/0x139
 [<ffffffff8117c35a>] proc_pid_readlink+0x6e/0xd9
 [<ffffffff81131202>] SyS_readlinkat+0x93/0xdc
 [<ffffffff81131266>] SyS_readlink+0x1b/0x1d
 [<ffffffff81473262>] system_call_fastpath+0x16/0x1b
---[ end trace a4b19d6c8a8b2eec ]---

Cheers,
Vinson

Eric W. Biederman (1):
  vfs: Remove incorrect debugging WARN in prepend_path

 fs/dcache.c |    9 ---------
 1 files changed, 0 insertions(+), 9 deletions(-)

[PATCH] vfs: Remove incorrect debugging WARN in prepend_path

[Vinson Lee]

From: Eric W. Biederman <ebiederm@xmission.com>

commit 93e3bce6287e1fb3e60d3324ed08555b5bbafa89 upstream.

The warning message in prepend_path is unclear and outdated.  It was
added as a warning that the mechanism for generating names of pseudo
files had been removed from prepend_path and d_dname should be used
instead.  Unfortunately the warning reads like a general warning,
making it unclear what to do with it.

Remove the warning.  The transition it was added to warn about is long
over, and I added code several years ago which in rare cases causes
the warning to fire on legitimate code, and the warning is now firing
and scaring people for no good reason.

Reported-by: Ivan Delalande <colona@arista.com>
Reported-by: Omar Sandoval <osandov@osandov.com>
Fixes: f48cfddc6729e ("vfs: In d_path don't call d_dname on a mount point")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
[ vlee: Backported to 3.10. Adjusted context. ]
Signed-off-by: Vinson Lee <vlee@twitter.com>
---
 fs/dcache.c |    9 ---------
 1 files changed, 0 insertions(+), 9 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 90be280..f1e8017 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2569,15 +2569,6 @@ static int prepend_path(const struct path *path,
 	return error;
 
 global_root:
-	/*
-	 * Filesystems needing to implement special "root names"
-	 * should do so with ->d_dname()
-	 */
-	if (IS_ROOT(dentry) &&
-	    (dentry->d_name.len != 1 || dentry->d_name.name[0] != '/')) {
-		WARN(1, "Root dentry has weird name <%.*s>\n",
-		     (int) dentry->d_name.len, dentry->d_name.name);
-	}
 	if (!slash)
 		error = prepend(buffer, buflen, "/", 1);
 	if (!error)
-- 
1.7.1