From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Jan Kara <jack@suse.cz>, Dave Chinner <dchinner@redhat.com>,
Jann Horn <jannh@google.com>, Christoph Hellwig <hch@lst.de>,
Oleg Nesterov <oleg@redhat.com>,
Kirill Shutemov <kirill@shutemov.name>,
Theodore Ts'o <tytso@mit.edu>,
Andrea Arcangeli <aarcange@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-nvdimm@lists.01.org, linux-ext4@vger.kernel.org,
linux-xfs@vger.kernel.org
Subject: Re: [PATCH 2/2] xfs: don't update mtime on COW faults
Date: Sat, 5 Sep 2020 08:36:52 -0700 [thread overview]
Message-ID: <20200905153652.GA7955@magnolia> (raw)
In-Reply-To: <alpine.LRH.2.02.2009050812060.12419@file01.intranet.prod.int.rdu2.redhat.com>
On Sat, Sep 05, 2020 at 08:13:02AM -0400, Mikulas Patocka wrote:
> When running in a dax mode, if the user maps a page with MAP_PRIVATE and
> PROT_WRITE, the xfs filesystem would incorrectly update ctime and mtime
> when the user hits a COW fault.
>
> This breaks building of the Linux kernel.
> How to reproduce:
> 1. extract the Linux kernel tree on dax-mounted xfs filesystem
> 2. run make clean
> 3. run make -j12
> 4. run make -j12
> - at step 4, make would incorrectly rebuild the whole kernel (although it
> was already built in step 3).
>
> The reason for the breakage is that almost all object files depend on
> objtool. When we run objtool, it takes COW page fault on its .data
> section, and these faults will incorrectly update the timestamp of the
> objtool binary. The updated timestamp causes make to rebuild the whole
> tree.
>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: stable@vger.kernel.org
>
> ---
> fs/xfs/xfs_file.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/fs/xfs/xfs_file.c
> ===================================================================
> --- linux-2.6.orig/fs/xfs/xfs_file.c 2020-09-05 10:01:42.000000000 +0200
> +++ linux-2.6/fs/xfs/xfs_file.c 2020-09-05 13:59:12.000000000 +0200
> @@ -1223,6 +1223,13 @@ __xfs_filemap_fault(
> return ret;
> }
>
> +static bool
> +xfs_is_write_fault(
Call this xfs_is_shared_dax_write_fault, and throw in the IS_DAX() test?
You might as well make it a static inline.
> + struct vm_fault *vmf)
> +{
> + return vmf->flags & FAULT_FLAG_WRITE && vmf->vma->vm_flags & VM_SHARED;
Also, is "shortcutting the normal fault path" the reason for ext2 and
xfs both being broken?
/me puzzles over why write_fault is always true for page_mkwrite and
pfn_mkwrite, but not for fault and huge_fault...
Also: Can you please turn this (checking for timestamp update behavior
wrt shared and private mapping write faults) into an fstest so we don't
mess this up again?
--D
> +}
> +
> static vm_fault_t
> xfs_filemap_fault(
> struct vm_fault *vmf)
> @@ -1230,7 +1237,7 @@ xfs_filemap_fault(
> /* DAX can shortcut the normal fault path on write faults! */
> return __xfs_filemap_fault(vmf, PE_SIZE_PTE,
> IS_DAX(file_inode(vmf->vma->vm_file)) &&
> - (vmf->flags & FAULT_FLAG_WRITE));
> + xfs_is_write_fault(vmf));
> }
>
> static vm_fault_t
> @@ -1243,7 +1250,7 @@ xfs_filemap_huge_fault(
>
> /* DAX can shortcut the normal fault path on write faults! */
> return __xfs_filemap_fault(vmf, pe_size,
> - (vmf->flags & FAULT_FLAG_WRITE));
> + xfs_is_write_fault(vmf));
> }
>
> static vm_fault_t
>
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next prev parent reply other threads:[~2020-09-05 15:37 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-03 19:24 a crash when running strace from persistent memory Mikulas Patocka
2020-09-03 19:55 ` Linus Torvalds
2020-09-04 8:08 ` Mikulas Patocka
2020-09-04 17:11 ` Linus Torvalds
2020-09-04 16:21 ` make misbehavior on ext2 in dax mode (was: a crash when running strace from persistent memory) Mikulas Patocka
2020-09-05 12:11 ` Mikulas Patocka
2020-09-05 12:12 ` [PATCH 1/2] ext2: don't update mtime on COW faults Mikulas Patocka
2020-09-07 9:00 ` Jan Kara
2020-09-05 12:13 ` [PATCH 2/2] xfs: " Mikulas Patocka
2020-09-05 15:36 ` Darrick J. Wong [this message]
2020-09-05 17:02 ` Mikulas Patocka
2020-09-10 6:06 ` Darrick J. Wong
2020-09-11 16:41 ` Mikulas Patocka
2020-09-05 16:47 ` Linus Torvalds
2020-09-05 17:03 ` Linus Torvalds
2020-09-07 8:59 ` Jan Kara
2020-09-05 17:04 ` [PATCH 2/2 v2] " Mikulas Patocka
2020-09-07 6:47 ` [PATCH 2/2] " Christoph Hellwig
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