Date: Wed, 21 Jul 2004 23:56:09 +0000 (UTC) From: Brian Feldman <green@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/vm vm_page.c Message-ID: <200407212356.i6LNu9Z6076388@repoman.freebsd.org>
next in thread | raw e-mail | index | archive | help
green 2004-07-21 23:56:09 UTC
FreeBSD src repository
Modified files:
sys/vm vm_page.c
Log:
Fix a race in vm_page_sleep_if_busy(). Due to vm_object locking
being incomplete, it currently has to know how to drop and pick back
up the vm_object's mutex if it has to sleep and drop the page queue
mutex. The problem with this is that if the page is busy, while we
are sleeping, the page can be freed and object disappear. When trying
to lock m->object, we'd get a stale or NULL pointer and crash.
The object is now cached, but this makes the assumption that
the object is referenced in some manner and will not itself
disappear while it is unlocked. Since this only happens if
the object is locked, I had to remove an assumption earlier in
contigmalloc() that reversed the order of locking the object and
doing vm_page_sleep_if_busy(), not the normal order.
Revision Changes Path
1.289 +12 -4 src/sys/vm/vm_page.c
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200407212356.i6LNu9Z6076388>