It Looks Like There's A Possible Data Corruption Bug For Btrfs Dating Back To 2009

[phoronix]

Phoronix: It Looks Like There's A Possible Data Corruption Bug For Btrfs Dating Back To 2009

A Phoronix reader pointed out to us this weekend there's been another Btrfs file-system data corruption bug discovered that dates back to around 2009...

http://www.phoronix.com/scan.php?page=news_item&px=Btrfs-Data-Bug-Hole-Read-Comp

[pal666]

"data corruption" here means that in some rare cases you could read garbage instead of region of zeros from file. it does not mean filesystem corruption

[yogi_berra]

"data corruption" here means that in some rare cases you could read garbage instead of region of zeros from file. it does not mean filesystem corruption

Well that is certainly comforting knowing your data is fucked instead of your file system.

[AsuMagic]

Well that is certainly comforting knowing your data is fucked instead of your file system.

is the data actually written correctly but only read wrong?

[macemoneta]

"data corruption" here means that in some rare cases you could read garbage instead of region of zeros from file. it does not mean filesystem corruption

Yes, I just read and interpreted it the same way. There is no corruption in the filesystem, but a possible error in reading the data if there is a compressed hole following an inline extent. It's apparently pretty rare, which is why it's low urgency.

[pal666]

is the data actually written correctly but only read wrong?

data aren't written at all, it is a file hole (region of zeroes)

[pal666]

Well that is certainly comforting knowing your data is fucked instead of your file system.

first, in case of filesystem corruption all your filesystem is fucked. second, in this case your data is intact, they are just not returned correctly in read call. this patch fixes read call and with it your data are returned correctly. and why do you call region of zeroes "data" lol

[starshipeleven]

MORE FLAME FOR THE FLAME GOD!!!!

Some facts:

This is kinda rare and affects only btrfs using zlib compression, uncompressed btrfs were fixed back in 2009 https://reviews.facebook.net/rUPSTRE...966bebafd80dd5

By default btrfs isn't using compression.

If you are running btrfs on RAID1, checksums would detect that, and data redundancy would fix it automatically on read.

[starshipeleven]

why do you call region of zeroes "data" lol

Couldn't there be valid data that is writing zeros to file and expects to return the same amount of zeros?

[AsuMagic]

Couldn't there be valid data that is writing zeros to file and expects to return the same amount of zeros?

if present files are not affected by this issue then that shouldn't cause an issue