CVS commit: src/sys/kern

["Emmanuel Dreyfus" <manu%netbsd.org@localhost>]

Module Name:    src
Committed By:   manu
Date:           Thu Sep 27 01:03:40 UTC 2018

Modified Files:
        src/sys/kern: vfs_trans.c

Log Message:
Work around deadlock between fstchg and fstcnt

When suspending a filesystem in fstrans_setstate(), we wait on
fstcnt for threads to finish transactions. While we do this, any
thread trying to start a filesystem transaction will wait on fstchg
in fstrans_start(), a situation which can deadlock.

The wait for fstcnt in fstrans_setstate() can be interrupted by
a signal, but the wait for fstchg in fstrans_start() cannot. Once
most processes are stuck in fstchg, it is impossible to send a
signal to the thread that waits on fstcnt, because no process
respond anymore to user input.

We fix that by adding a timeout to the wait on fstcnt in
fstrans_setstate(). This means suspending a filesystem may fail,
but it was already the case when the sleep was interupted by
a signal, hence calling function must already handle a possible
failure.

Fixes kern/53624


To generate a diff of this commit:
cvs rdiff -u -r1.48 -r1.49 src/sys/kern/vfs_trans.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.