** Changed in: intel
Status: Triaged => Fix Released
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https://bugs.launchpad.net/bugs/1789146
Title:
[Bug][CLX]assertion failure with util_range_rw using libpmemlog,
possible kernel DAX bug
Status in intel:
Fix Released
Status in linux package in Ubuntu:
Fix Released
Bug description:
Description:
On Mon, Apr 16, 2018 at 8:20 AM, Czurylo, Krzysztof
<[email protected]> wrote:
>
> I suspect the problem is caused by a bug in the kernel.
>
> I did a few experiments and it looks like the issue occurs only if the
> filesystem is mounted with "-o dax". I can reproduce is both for xfs
> and ext4, so it's not FS-specific, but rather DAX-specific. It also
> reproduces on an emulated PMEM - no need to use real AEP DIMMs.
>
> Using the latest kernel (4.16.0) does not help.
>
> What happens:
>
> In debug version of libpmemlog (but also libpmemblk), the entire pool
> is by default write-protected with mprotect(..., PROT_READ).
>
> When the program attempts to write some data to the pool (i.e.
> pmemlog_append, pmemblk_write, ...), the library unprotects the pages
> to be modified (usually just one or two pages) and once the data is
> stored, the pages are protected again.
>
> Inside the kernel, mprotect splits the memory region associated with
> the pool into 3 regions: the read-only head and tail + one r/w page in
> the middle.
>
> The problem is that after the last step, the memory region associated
> with the modified page is not merged with the adjacent regions having
> the same protection flags (ro) to form one big read-only region again.
> This leads to the situation where we have thousands of 4K memory
> mappings per process that are tracked by the kernel separately. When
> the number of maps exceeds the limit (default is 65536 - see:
> /proc/sys/vm/max_map_count), mprotect fails with ENOMEM, which aborts
> the program.
Commitid: e1fb4a0864958fac2fb1b23f9f4562a9f90e3e8f
dax: remove VM_MIXEDMAP for fsdax and device dax
Target Kernel: 4.19
Target Release: 18.10
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