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Date:	Mon, 13 Sep 2010 14:20:11 -0700
From:	Earl Chew <echew AT ixiacom DOT com>
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To:	<cygwin AT cygwin DOT com>
Subject:	Deletion race in NtSetFileInformation ? (Directory not empty error in rm -r -f)
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I have a Makefile which performs "rm -f -r" as part of a clean target.
On Win7 with 1.7.5-1 this can fail with:

rm -f -r win32
rm: cannot remove directory `win32': Directory not empty


I tried 1.7.7-1 but the problem still seems to be there.


Doing a little digging, I find that /bin/rm calls
unlinkat("win32/dll"), which eventually calls unlink_nt().


A short time later, /bin/rm calls unlink_at("win32") and
fails at check_dir_not_empty() because it finds the following
entries::

 413407 [main] rm 3612 check_dir_not_empty: File name: 2 0x2E 0x610E 0x10 "."
 413493 [main] rm 3612 check_dir_not_empty: File name: 4 0x2E 0x2E 0x18   ".."
 413574 [main] rm 3612 check_dir_not_empty: File name: 6 0x64 0x6C 0x6C   "dll"

Huh?  Wasn't this the directory that was just deleted?

Taking a look in the directory after the fact shows that the parent directory
appears to be empty :

W:> dir win32
 Volume in drive W is OS
 Volume Serial Number is C0E0-BBEE

 Directory of W:\cerberus\acl\col_\ato\win32

13/09/2010  01:57 PM    <DIR>          .
13/09/2010  01:57 PM    <DIR>          ..
               0 File(s)              0 bytes
               2 Dir(s)  392,720,297,984 bytes free


Hmm ... my reading of unlink_nt() is that the directory "win32/dll"
is deleted by setting FileDispositionInformation via NtSetFileInformation().

Since the file entry seems to be found during the subsequent check_dir_not_empty()
call when trying to delete the parent directory, is some form
of explicit synchronisation required when deleting
the child "win32/dll" to be sure that the deletion is
actually complete?


Earl

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