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/>
index | next in thread | raw e-mail
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=237588 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. 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 the 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 pages that were part of the write. 4) If any bytes were written by step 2 and invalidated but not written by step 3, then they will be lost. Steps to reproduce: ================== 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 -- You are receiving this mail because: You are the assignee for the bug.help
Want to link to this message? Use this
URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-237588-227>