Date: Tue, 12 Mar 2019 19:08:49 +0000 From: bugzilla-noreply@freebsd.org To: fs@FreeBSD.org Subject: [Bug 230962] Kernel panic when writing extended attributes with soft updates enabled Message-ID: <bug-230962-3630-1SuyHb3T32@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-230962-3630@https.bugs.freebsd.org/bugzilla/> References: <bug-230962-3630@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D230962 --- Comment #18 from commit-hook@freebsd.org --- A commit references this bug: Author: mckusick Date: Tue Mar 12 19:08:42 UTC 2019 New revision: 345077 URL: https://svnweb.freebsd.org/changeset/base/345077 Log: This is an additional fix for bug report 230962. When using extended attributes, the kernel can panic with either "ffs_truncate3" or with "softdep_deallocate_dependencies: dangling deps". The problem arises because the flushbuflist() function which is called to clear out buffers is passed either the V_NORMAL flag to indicate that it should flush buffer associated with the contents of the file or the V_ALT flag to indicate that it should flush the buffers associated with the extended attribute data. The buffers containing the extended attribute data are identified by having their BX_ALTDATA flag set in the buffer's b_xflags field. The BX_ALTDATA flag is set on the buffer when the extended attribute block is first allocated or when its contents are read in from the disk. On a busy system, a buffer may be reused for another purpose, but the contents of the block that it contained continues to be held in the main page cache. Each physical page is identified as holding the contents of a logical block within a specified file (identified by a vnode). When a request is made to read a file, the kernel first looks for the block in the existing buffers. If it is not found there, it checks the page cache to see if it is still there. If it is found in the page cache, then it is remapped into a new buffer thus avoiding the need to read it in from the disk. The bug is that when a buffer request made for an extended attribute is fulfilled by reconstituting a buffer from the page cache rather than reading it in from disk, the BX_ALTDATA flag was not being set. Thus the flushbuflist() function would never clear it out and the "ffs_truncate3" panic would occur because the vnode being cleared still had buffers on its clean-buffer list. If the extended attribute was being updated, it is first read, then updated, and finally written. If the read is fulfilled by reconstituting the buffer from the page cache the BX_ALTDATA flag was not set and thus the dirty buffer would never be flushed by flushbuflist(). Eventually the buffer would be recycled. Since it was never written it would have an unfinished dependency which would trigger the "softdep_deallocate_dependencies: dangling deps" panic. The fix is to ensure that the BX_ALTDATA flag is set when a buffer has been reconstituted from the page cache. PR: 230962 Reported by: 2t8mr7kx9f@protonmail.com Reviewed by: kib Tested by: Peter Holm MFC after: 1 week Sponsored by: Netflix Changes: head/sys/kern/vfs_bio.c --=20 You are receiving this mail because: You are the assignee for the bug.=
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