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Date: Thu, 13 Jun 2013 10:16:29 -0400
From: Peter Hurley <peter@...leysoftware.com>
To: Markus Trippelsdorf <markus@...ppelsdorf.de>
CC: Mikael Pettersson <mikpe@...uu.se>, linux-kernel@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.cz>,
David Howells <dhowells@...hat.com>,
Orion Poplawski <orion@...a.nwra.com>
Subject: Re: Strange intermittent EIO error when writing to stdout since v3.8.0
On 06/13/2013 06:39 AM, Markus Trippelsdorf wrote:
> On 2013.06.07 at 20:22 +0200, Mikael Pettersson wrote:
>> Peter Hurley writes:
>> > Based on the other reports from Mikael and David, I suspect this problem
>> > may have to do with my commit 699390354da6c258b65bf8fa79cfd5feaede50b6:
>> >
>> > pty: Ignore slave pty close() if never successfully opened
>> >
>> > This commit poisons the pty under certain error conditions that may
>> > occur from parallel open()s (or parallel close() with pending write()).
>> >
>> > It's unclear to me which error condition is triggered and how user-space
>> > got an open file descriptor but that seems the most likely. Is the problem
>> > reproducible enough that a debug patch would likely trigger?
>>
>> In my case the problem occurred frequently enough that I've been forced
>> to change my build procedures to avoid it. I'd welcome a debug patch.
>
> Since apparently no debugging patch is forthcoming, maybe it's time to
> test the simple revert of commit 699390354da.
I apologize for the delay.
Here's a debug patch which I hope will narrow down the circumstances of
this error condition.
Regards,
Peter Hurley
PS - Don't get excited about EIO from read() which you will see during
boot. That's expected when the slave closes and the master is parked on
a blocking read().
--- >% ---
Subject: [PATCH] tty: Debug EIO from write()
Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
drivers/tty/pty.c | 22 +++++++++++++++++++---
drivers/tty/tty_io.c | 51 ++++++++++++++++++++++++++++++++++++++++++---------
2 files changed, 61 insertions(+), 12 deletions(-)
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 9c2f1bc..2ce2bb2 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -25,6 +25,16 @@
#include <linux/slab.h>
#include <linux/mutex.h>
+#define TTY_DEBUG_EIO 1
+
+#ifdef TTY_DEBUG_EIO
+#define tty_debug_eio(tty, f, args...) ({ \
+ char __b[64]; \
+ printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \
+})
+#else
+#define tty_debug_eio(tty, f, args...)
+#endif
#ifdef CONFIG_UNIX98_PTYS
static struct tty_driver *ptm_driver;
@@ -246,12 +256,18 @@ static int pty_open(struct tty_struct *tty, struct file *filp)
set_bit(TTY_IO_ERROR, &tty->flags);
retval = -EIO;
- if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
+ if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) {
+ tty_debug_eio(tty, "other pty closed (%#lx)\n", tty->flags);
goto out;
- if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
+ }
+ if (test_bit(TTY_PTY_LOCK, &tty->link->flags)) {
+ tty_debug_eio(tty, "ptm still locked\n");
goto out;
- if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1)
+ }
+ if (tty->driver->subtype == PTY_TYPE_SLAVE && tty->link->count != 1) {
+ tty_debug_eio(tty, "ptm open count (%d)\n", tty->link->count);
goto out;
+ }
clear_bit(TTY_IO_ERROR, &tty->flags);
clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 62e942d..e71c61f 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -105,11 +105,21 @@
#include <linux/kmod.h>
#include <linux/nsproxy.h>
-#undef TTY_DEBUG_HANGUP
+#define TTY_DEBUG_HANGUP 1
+#define TTY_DEBUG_EIO 1
#define TTY_PARANOIA_CHECK 1
#define CHECK_TTY_COUNT 1
+#ifdef TTY_DEBUG_EIO
+#define tty_debug_eio(tty, f, args...) ({ \
+ char __b[64]; \
+ printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \
+})
+#else
+#define tty_debug_eio(tty, f, args...)
+#endif
+
struct ktermios tty_std_termios = { /* for the benefit of tty drivers */
.c_iflag = ICRNL | IXON,
.c_oflag = OPOST | ONLCR,
@@ -424,6 +434,7 @@ int tty_check_change(struct tty_struct *tty)
if (is_ignored(SIGTTOU))
goto out;
if (is_current_pgrp_orphaned()) {
+ tty_debug_eio(tty, "pgrp orphaned?? (%#lx)\n", tty->flags);
ret = -EIO;
goto out;
}
@@ -448,6 +459,9 @@ static ssize_t hung_up_tty_read(struct file *file, char __user *buf,
static ssize_t hung_up_tty_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
+ struct tty_struct *tty = file_tty(file);
+
+ tty_debug_eio(tty, "%#lx\n", tty ? tty->flags : -1L);
return -EIO;
}
@@ -1020,16 +1034,22 @@ static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
if (tty_paranoia_check(tty, inode, "tty_read"))
return -EIO;
- if (!tty || (test_bit(TTY_IO_ERROR, &tty->flags)))
+ if (!tty || (test_bit(TTY_IO_ERROR, &tty->flags))) {
+ tty_debug_eio(tty, "%#lx\n", tty ? tty->flags : -1L);
return -EIO;
+ }
/* We want to wait for the line discipline to sort out in this
situation */
ld = tty_ldisc_ref_wait(tty);
- if (ld->ops->read)
+ if (ld->ops->read) {
i = (ld->ops->read)(tty, file, buf, count);
- else
+ if (i == -EIO)
+ tty_debug_eio(tty, "ldisc error (%#lx)\n", tty->flags);
+ } else {
+ tty_debug_eio(tty, "no ldisc read method???\n");
i = -EIO;
+ }
tty_ldisc_deref(ld);
if (i > 0)
@@ -1197,18 +1217,31 @@ static ssize_t tty_write(struct file *file, const char __user *buf,
if (tty_paranoia_check(tty, file_inode(file), "tty_write"))
return -EIO;
- if (!tty || !tty->ops->write ||
- (test_bit(TTY_IO_ERROR, &tty->flags)))
- return -EIO;
+ if (!tty || !tty->ops->write || (test_bit(TTY_IO_ERROR, &tty->flags))) {
+ if (tty && !tty->ops->write)
+ tty_debug_eio(tty, "no driver write method???\n");
+ else
+ tty_debug_eio(tty, "%#lx\n", tty ? tty->flags : -1L);
+ return -EIO;
+ }
/* Short term debug to catch buggy drivers */
if (tty->ops->write_room == NULL)
printk(KERN_ERR "tty driver %s lacks a write_room method.\n",
tty->driver->name);
ld = tty_ldisc_ref_wait(tty);
- if (!ld->ops->write)
+ if (!ld->ops->write) {
+ tty_debug_eio(tty, "no ldisc write method???\n");
ret = -EIO;
- else
+ } else {
ret = do_tty_write(ld->ops->write, tty, file, buf, count);
+ if (ret == -EIO) {
+ if (tty_hung_up_p(file))
+ tty_debug_eio(tty, "hung up\n");
+ else
+ tty_debug_eio(tty, "ldisc error: flags=%#lx count=%d other=%d\n",
+ tty->flags, tty->count, tty->link ? tty->link->count : -1);
+ }
+ }
tty_ldisc_deref(ld);
return ret;
}
--
1.8.1.2
--
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