Commit ecc0c469 authored Nov 17, 2017 by NeilBrown Committed by Linus Torvalds Nov 17, 2017

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.

It isn't a crash or a data corruption, but having autofs mountpoints
suddenly stop working is rather inconvenient.

Ian said:

: And given the problems with a half dozen (or so) user space applications
: consuming large amounts of CPU under heavy mount and umount activity this
: could happen more easily than we expect.

Link: http://lkml.kernel.org/r/87y3norvgp.fsf@notabene.neil.brown.name


Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: Ian Kent <raven@themaw.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent e4f02fda

fs/autofs4/waitq.c

+14 −1

Original line number	Diff line number	Diff line
		@@ -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);
		}

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