Date: Fri, 26 Apr 2019 20:47:59 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 237588] [fusefs] data corruption when mixing normal writes and mmap writes with Write-through cache mode Message-ID: <bug-237588-227@https.bugs.freebsd.org/bugzilla/>
next in thread | raw e-mail | index | archive | help
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D237588 Bug ID: 237588 Summary: [fusefs] data corruption when mixing normal writes and mmap writes with Write-through cache mode Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Many People Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: asomers@FreeBSD.org fusefs supports three cache modes: uncached, write-through, and writeback.= =20 Write-through is the default. However, as currently implemented it's more = like "write-around" than true "write-through". That is, writes go directly to t= he fuse daemon and invalidate the cache, rather than fill it. This is merely a performance bug when using normal writes (write(2), pwrite= (2), aio_write(2), etc). But when mixing normal writes with mmap()'ed writes, it causes data corruption. The sequence goes like this: 1) A process mmaps a fusefs file 2) That process writes some data, but does not msync() it. 3) A process writes directly, such as with write(2) to a region of the file that overlaps what was written in step 2. fusefs invalidates all cached pa= ges that were part of the write. 4) If any bytes were written by step 2 and invalidated but not written by s= tep 3, then they will be lost. Steps to reproduce: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D 1) Build the passthrough example from sysutils/libfuse and fsx from tools/regression/fsx 2) mkdir -p /tmp/mnt 3) /path/to/libfuse/build/example/passthrough -d /tmp/mnt 4) /path/to/fsx/fsx -P /tmp -S1333 -b5 -N 15 -U fsx.bin --=20 You are receiving this mail because: You are the assignee for the bug.=
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-237588-227>