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Subject: RE: [PATCH] fs: fat: add check for dir size in fat_calc_dir_size
Reply-To: anupam.al@samsung.com
From:   Anupam Aggarwal <anupam.al@samsung.com>
To:     OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
        AMIT SAHRAWAT <a.sahrawat@samsung.com>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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Date:   Fri, 03 Jul 2020 19:59:39 +0530
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Hi Ogawa,

>So what was the root cause of slowness on big directory?

Problem happened on FAT32 formatted 32GB USB 3.0 pendrive, which has 20GB o=
f data, cluster size is 16KB
It has one corrupted directory whose size calculated by fat_calc_dir_size()=
 is 1146896384 bytes i.e. 1.06 GB.

When directory traversal of corrupted directory starts, directory entries l=
ooks to be corrupted
and lookup fails for these directory entries.
Some directory entries name are having format abc/xyz,
following are the few observed directory entry names:

eqk/hb*
*=C3=B9=C3=AF/=C3=B2=C2=A27=C3=B4.=C3=BAB=C3=A6=0D=0Aty7=40o/<=60=0D=0A-=C3=
=B2%/=C3=A73=7B.9q=0D=0A'=C3=BBu/=C3=B6y<=C3=B6.=5Em=C3=B6=0D=0APh=E2=95=A4=
Cf=E2=94=8C6g.=C3=9F/k=0D=0A=0D=0ANow=20when=20path=20lookup=20happens=20fo=
r=20above=20directory=20entries,=20it=20will=20search=20for=20name=20before=
=20=E2=80=98/=E2=80=99=20in=20corrupted=20directory=20e.g.=0D=0A=0D=0Aeqk=
=0D=0A*=C3=B9=C3=AF=0D=0Aty7=40o=0D=0A-=C3=B2%=0D=0A'=C3=BBu=0D=0APh=E2=95=
=A4Cf=E2=94=8C6g.=C3=9F=0D=0A=0D=0AThere=20are=20also=20directory=20entries=
=20with=20garbage=20name=20for=20which=20lookup=20fails,=20e.g.=0D=0A=C3=A1=
)Y=C2=BA&q=C2=BC(.=C3=AE=C2=BB.=0D=0A=C3=86=E2=88=9E=E2=94=B4=C3=87=E2=96=
=80=E2=95=9Cr=E2=95=9F.=E2=95=A3g=C2=BD=0D=0A4=E2=96=92h1=E2=96=93x0=E2=94=
=A4.p3=E2=95=A3=0D=0A=0D=0ADuring=20search=20for=20single=20name=20in=20fat=
_search_long()=20function,=20whole=20corrupted=20directory=20of=20size=201.=
06GB=20is=20traversed,=0D=0Awhich=20takes=20around=20230=20to=20240=20secs,=
=20which=20finally=20ends=20up=20with=20returning=20ENOENT.=0D=0A=0D=0ANow=
=20multiple=20lookups=20in=20corrupted=20directory=20makes=20=E2=80=9Cls=20=
-lR=E2=80=9D=20never-ending=20e.g.=20in=20overnite=20test=20of=20running=20=
=E2=80=9Cls=20=E2=80=93lR=E2=80=9D=0D=0Aon=20USB=20having=20corrupted=20dir=
ectory,=20around=20200=20such=20lookups=20in=20corrupted=20directory=20took=
=2014hrs=20and=20still=20=E2=80=9Dls=20=E2=80=93lR=E2=80=9D=20is=20running.=
=0D=0A=0D=0ATotal=20number=20of=20directory=20entries=20in=20corrupted=20di=
rectory=20of=20size=201146896384=20bytes=20=3D=201146896384/32=20=3D=203584=
0512,=0D=0Aso=20lookup=20for=2035840512=20looks=20very=20exhaustive,=20ther=
efore=20we=20have=20put=20size=20check=20of=20directory=20in=20fat_calc_dir=
_size()=0D=0Aand=20prevented=20the=20directory=20traversal=20by=20returning=
=20-EIO.=0D=0A=0D=0AWhile=20browsing=20corrupted=20directory(=5CCorruptedDI=
R)=20on=20Windows=2010=20PC,=0D=0A2623=20directory=20entries=20were=20liste=
d=20and=20timestamps=20were=20wrong=0D=0A=0D=0AFollowing=20is=20the=20reado=
nly=20chkdsk=20output=20of=20USB.=0D=0A=0D=0A------------------------------=
--------------------------------------------------------=0D=0Achkdsk=20I:=
=0D=0AThe=20type=20of=20the=20file=20system=20is=20FAT32.=0D=0AVolume=20AAA=
=20created=2012/28/2018=203:15=20PM=0D=0AVolume=20Serial=20Number=20is=2016=
06-72DC=0D=0AWindows=20is=20verifying=20files=20and=20folders...=0D=0AWindo=
ws=20found=20errors=20on=20the=20disk,=20but=20will=20not=20fix=20them=0D=
=0Abecause=20disk=20checking=20was=20run=20without=20the=20/F=20(fix)=20par=
ameter.=0D=0AThe=20=5C=24TXRAJNL.DAT=20entry=20contains=20a=20nonvalid=20li=
nk.=0D=0AThe=20size=20of=20the=20=5C=24TXRAJNL.DAT=20entry=20is=20not=20val=
id.=0D=0AUnrecoverable=20error=20in=20folder=20=5CCorruptedDIR.=0D=0AConver=
t=20folder=20to=20file=20(Y/N)?=20n=0D=0AThe=20=5CBBB=5Cfile1.txt=20entry=
=20contains=20a=20nonvalid=20link.=0D=0AThe=20size=20of=20the=20=5CBBB=5Cfi=
le1.txt=20entry=20is=20not=20valid.=0D=0AThe=20=5CCCC=5Cfile1.txt=20entry=
=20contains=20a=20nonvalid=20link.=0D=0AThe=20size=20of=20the=20=5CCCC=5Cfi=
le1.txt=20entry=20is=20not=20valid.=0D=0AFile=20and=20folder=20verification=
=20is=20complete.=0D=0AConvert=20lost=20chains=20to=20files=20(Y/N)?=20n=0D=
=0A3531520=20KB=20of=20free=20disk=20space=20would=20be=20added.=0D=0A=0D=
=0AWindows=20has=20checked=20the=20file=20system=20and=20found=20problems.=
=0D=0ARun=20CHKDSK=20with=20the=20/F=20(fix)=20option=20to=20correct=20thes=
e.=0D=0A=20=20=2030,015,472=20KB=20total=20disk=20space.=0D=0A=20=20=20=20=
=20=20=20=20=20=20400=20KB=20in=202=20hidden=20files.=0D=0A=20=20=20=20=20=
=20=20=202,800=20KB=20in=2048=20folders.=0D=0A=20=20=2016,479,312=20KB=20in=
=207,583=20files.=0D=0A=20=20=20=209,999,392=20KB=20are=20available.=0D=0A=
=0D=0A=20=20=20=20=20=20=2016,384=20bytes=20in=20each=20allocation=20unit.=
=0D=0A=20=20=20=201,875,967=20total=20allocation=20units=20on=20disk.=0D=0A=
=20=20=20=20=20=20624,962=20allocation=20units=20available=20on=20disk.=0D=
=0A------------------------------------------------------------------------=
--------------=0D=0A=0D=0APlease=20let=20us=20know=20for=20any=20queries,=
=0D=0Aand=20please=20suggest=20if=20something=20better=20can=20be=20done.=
=0D=0A=0D=0ARegards,=0D=0AAnupam=0D=0A