Date: Fri, 21 Feb 2003 16:59:34 -0800 (PST) From: Kirk McKusick <mckusick@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/ufs/ffs ffs_snapshot.c Message-ID: <200302220059.h1M0xYEr074756@repoman.freebsd.org>
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mckusick 2003/02/21 16:59:34 PST
Modified files:
sys/ufs/ffs ffs_snapshot.c
Log:
This patch fixes a deadlock between the bufdaemon and a process taking
a snapshot. As part of taking a snapshot of a filesystem, the kernel
builds up a list of the filesystem metadata (such as the cylinder
group bitmaps) that are contained in the snapshot. When doing a
copy-on-write check, the list is first consulted. If the block being
written is found on the list, then the full snapshot lookup can be
avoided. Besides providing an important performance speedup this
check also avoids a potential deadlock between the code creating
the snapshot and the bufdaemon trying to cleanup snapshot related
buffers. This fix creates a temporary list containing the key
metadata blocks that can cause the deadlock. This temporary list
is used between the time that the snapshot is first enabled and the
time that the fully complete list is built.
Reported by: Attila Nagy <bra@fsn.hu>
Sponsored by: DARPA & NAI Labs.
Revision Changes Path
1.62 +43 -7 src/sys/ufs/ffs/ffs_snapshot.c
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