linux-kernel - [PATCH] autofs: don't fail mount for transient error

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Date:   Fri, 03 Nov 2017 12:40:06 +1100
From:   NeilBrown <neilb@...e.com>
To:     Ian Kent <raven@...maw.net>,
        Andrew Morton <akpm@...ux-foundation.org>
cc:     lkml <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org
Subject: [PATCH] autofs: don't fail mount for transient error

Currently if the autofs kernel module gets an error when
writing to the pipe which links to the daemon, then it
marks the whole moutpoint as catatonic, and it will stop working.

It is possible that the error is transient.  This can happen
if the daemon is slow and more than 16 requests queue up.
If a subsequent process tries to queue a request, and is then signalled,
the write to the pipe will return -ERESTARTSYS and autofs
will take that as total failure.

So change the code to assess -ERESTARTSYS and -ENOMEM as transient
failures which only abort the current request, not the whole
mountpoint.

Signed-off-by: NeilBrown <neilb@...e.com>
---

Do people think this should got to -stable ??
It isn't a crash or a data corruption, but having autofs mountpoints
suddenly stop working is rather inconvenient.

Thanks,
NeilBrown

 fs/autofs4/waitq.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index 4ac49d038bf3..8fc41705c7cd 100644
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -81,7 +81,8 @@ static int autofs4_write(struct autofs_sb_info *sbi,
 		spin_unlock_irqrestore(&current->sighand->siglock, flags);
 	}

-	return (bytes > 0);
+	/* if 'wr' returned 0 (impossible) we assume -EIO (safe) */
+	return bytes == 0 ? 0 : wr < 0 ? wr : -EIO;
 }

 static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
@@ -95,6 +96,7 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
 	} pkt;
 	struct file *pipe = NULL;
 	size_t pktsz;
+	int ret;

 	pr_debug("wait id = 0x%08lx, name = %.*s, type=%d\n",
 		 (unsigned long) wq->wait_queue_token,
@@ -169,7 +171,18 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
 	mutex_unlock(&sbi->wq_mutex);

 	if (autofs4_write(sbi, pipe, &pkt, pktsz))
+	switch (ret = autofs4_write(sbi, pipe, &pkt, pktsz)) {
+	case 0:
+		break;
+	case -ENOMEM:
+	case -ERESTARTSYS:
+		/* Just fail this one */
+		autofs4_wait_release(sbi, wq->wait_queue_token, ret);
+		break;
+	default:
 		autofs4_catatonic_mode(sbi);
+		break;
+	}
 	fput(pipe);
 }

-- 
2.14.0.rc0.dirty

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