[v2,1/1] fsmonitor: don't fill bitmap with entries to be removed
diff mbox series

Message ID 08741d986c2b51828f115ab50f178d62e9982978.1570654810.git.gitgitgadget@gmail.com
State New
Headers show
Series
  • fsmonitor: don't fill bitmap with entries to be removed
Related show

Commit Message

Derrick Stolee via GitGitGadget Oct. 9, 2019, 9 p.m. UTC
From: William Baker <William.Baker@microsoft.com>

While doing some testing with fsmonitor enabled I found
that git commands would segfault after staging and
unstaging an untracked file.  Looking at the crash it
appeared that fsmonitor_ewah_callback was attempting to
adjust bits beyond the bounds of the index cache.

Digging into how this could happen it became clear that
the fsmonitor extension must have been written with
more bits than there were entries in the index.  The
root cause ended up being that fill_fsmonitor_bitmap was
populating fsmonitor_dirty with bits for all entries in
the index, even those that had been marked for removal.

To solve this problem fill_fsmonitor_bitmap has been
updated to skip entries with the the CE_REMOVE flag set.
With this change the bits written for the fsmonitor
extension will be consistent with the index entries
written by do_write_index.  Additionally, BUG checks
have been added to detect if the number of bits in
fsmonitor_dirty should ever exceed the number of
entries in the index again.

Another option that was considered was moving the call
to fill_fsmonitor_bitmap closer to where the index is
written (and where the fsmonitor extension itself is
written).  However, that did not work as the
fsmonitor_dirty bitmap must be filled before the index
is split during writing.

Signed-off-by: William Baker <William.Baker@microsoft.com>
---
 fsmonitor.c                 | 29 ++++++++++++++++++++++++-----
 t/t7519-status-fsmonitor.sh | 13 +++++++++++++
 t/t7519/fsmonitor-env       | 24 ++++++++++++++++++++++++
 3 files changed, 61 insertions(+), 5 deletions(-)
 create mode 100755 t/t7519/fsmonitor-env

Comments

SZEDER Gábor Oct. 10, 2019, 11:07 a.m. UTC | #1
On Wed, Oct 09, 2019 at 02:00:12PM -0700, William Baker via GitGitGadget wrote:
> diff --git a/t/t7519-status-fsmonitor.sh b/t/t7519-status-fsmonitor.sh
> index 81a375fa0f..87042470ab 100755
> --- a/t/t7519-status-fsmonitor.sh
> +++ b/t/t7519-status-fsmonitor.sh
> @@ -354,4 +354,17 @@ test_expect_success 'discard_index() also discards fsmonitor info' '
>  	test_cmp expect actual
>  '
>  
> +# This test covers staging/unstaging files that appear at the end of the index.
> +# Test files with names beginning with 'z' are used under the assumption that
> +# earlier tests do not add/leave index entries that sort below them. 
> +test_expect_success 'status succeeds after staging/unstaging ' '
> +	test_commit initial &&

This is confusing: this is the 29th test case in this script and it
creates an "initial" commit?!

The first "setup" test case has already created an initial commit, so
this should rather be called "second".

OTOH, none of the later commands in this test case seem to have
anything to do with this second commit, and indeed the test case works
even without it (i.e. 'git status' still segfaults without the fix and
then succeeds with the fix applied), so instead of updating its
message perhaps it could simply be removed.

> +	removed=$(test_seq 1 100 | sed "s/^/z/") &&
> +	touch $removed &&
> +	git add $removed &&
> +	test_config core.fsmonitor "$TEST_DIRECTORY/t7519/fsmonitor-env" &&
> +	FSMONITOR_LIST="$removed" git restore -S $removed &&
> +	FSMONITOR_LIST="$removed" git status
> +'
> +
>  test_done
SZEDER Gábor Oct. 10, 2019, 11:22 a.m. UTC | #2
On Thu, Oct 10, 2019 at 01:07:32PM +0200, SZEDER Gábor wrote:
> On Wed, Oct 09, 2019 at 02:00:12PM -0700, William Baker via GitGitGadget wrote:
> > diff --git a/t/t7519-status-fsmonitor.sh b/t/t7519-status-fsmonitor.sh
> > index 81a375fa0f..87042470ab 100755
> > --- a/t/t7519-status-fsmonitor.sh
> > +++ b/t/t7519-status-fsmonitor.sh
> > @@ -354,4 +354,17 @@ test_expect_success 'discard_index() also discards fsmonitor info' '
> >  	test_cmp expect actual
> >  '
> >  
> > +# This test covers staging/unstaging files that appear at the end of the index.
> > +# Test files with names beginning with 'z' are used under the assumption that
> > +# earlier tests do not add/leave index entries that sort below them. 

I just read through Junio's comments on the first version of this
patch, in particular his remarks about this comment.

If this new test case below were run in a dedicated repository, then
this comment wouldn't be necessary, and all my comments below about
that not-really-initial commit would be moot, too.

> > +test_expect_success 'status succeeds after staging/unstaging ' '
> > +	test_commit initial &&
> 
> This is confusing: this is the 29th test case in this script and it
> creates an "initial" commit?!
> 
> The first "setup" test case has already created an initial commit, so
> this should rather be called "second".
> 
> OTOH, none of the later commands in this test case seem to have
> anything to do with this second commit, and indeed the test case works
> even without it (i.e. 'git status' still segfaults without the fix and
> then succeeds with the fix applied), so instead of updating its
> message perhaps it could simply be removed.

> 
> > +	removed=$(test_seq 1 100 | sed "s/^/z/") &&
> > +	touch $removed &&
> > +	git add $removed &&
> > +	test_config core.fsmonitor "$TEST_DIRECTORY/t7519/fsmonitor-env" &&
> > +	FSMONITOR_LIST="$removed" git restore -S $removed &&
> > +	FSMONITOR_LIST="$removed" git status
> > +'
> > +
> >  test_done
William Baker Oct. 11, 2019, 4:38 p.m. UTC | #3
On 10/10/19 4:22 AM, SZEDER Gábor wrote:
>>> +# This test covers staging/unstaging files that appear at the end of the index.
>>> +# Test files with names beginning with 'z' are used under the assumption that
>>> +# earlier tests do not add/leave index entries that sort below them. 
> 
> I just read through Junio's comments on the first version of this
> patch, in particular his remarks about this comment.
> 
> If this new test case below were run in a dedicated repository, then
> this comment wouldn't be necessary, and all my comments below about
> that not-really-initial commit would be moot, too.
> 

Thanks for this suggestion!  I will submit a v3 version of the patch
with an update to the test script.

- William

Patch
diff mbox series

diff --git a/fsmonitor.c b/fsmonitor.c
index 231e83a94d..7e27839278 100644
--- a/fsmonitor.c
+++ b/fsmonitor.c
@@ -14,8 +14,13 @@  struct trace_key trace_fsmonitor = TRACE_KEY_INIT(FSMONITOR);
 static void fsmonitor_ewah_callback(size_t pos, void *is)
 {
 	struct index_state *istate = (struct index_state *)is;
-	struct cache_entry *ce = istate->cache[pos];
+	struct cache_entry *ce;
+	
+	if (pos >= istate->cache_nr)
+		BUG("fsmonitor_dirty has more entries than the index (%"PRIuMAX" >= %u)",
+		    (uintmax_t)pos, istate->cache_nr);
 
+	ce = istate->cache[pos];
 	ce->ce_flags &= ~CE_FSMONITOR_VALID;
 }
 
@@ -50,17 +55,24 @@  int read_fsmonitor_extension(struct index_state *istate, const void *data,
 	}
 	istate->fsmonitor_dirty = fsmonitor_dirty;
 
+	if (istate->fsmonitor_dirty->bit_size > istate->cache_nr)
+		BUG("fsmonitor_dirty has more entries than the index (%"PRIuMAX" > %u)",
+		    (uintmax_t)istate->fsmonitor_dirty->bit_size, istate->cache_nr);
+
 	trace_printf_key(&trace_fsmonitor, "read fsmonitor extension successful");
 	return 0;
 }
 
 void fill_fsmonitor_bitmap(struct index_state *istate)
 {
-	unsigned int i;
+	unsigned int i, skipped = 0;
 	istate->fsmonitor_dirty = ewah_new();
-	for (i = 0; i < istate->cache_nr; i++)
-		if (!(istate->cache[i]->ce_flags & CE_FSMONITOR_VALID))
-			ewah_set(istate->fsmonitor_dirty, i);
+	for (i = 0; i < istate->cache_nr; i++) {
+		if (istate->cache[i]->ce_flags & CE_REMOVE)
+			skipped++;
+		else if (!(istate->cache[i]->ce_flags & CE_FSMONITOR_VALID))
+			ewah_set(istate->fsmonitor_dirty, i - skipped);
+	}
 }
 
 void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate)
@@ -71,6 +83,10 @@  void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate)
 	uint32_t ewah_size = 0;
 	int fixup = 0;
 
+	if (istate->fsmonitor_dirty->bit_size > istate->cache_nr)
+		BUG("fsmonitor_dirty has more entries than the index (%"PRIuMAX" > %u)",
+		    (uintmax_t)istate->fsmonitor_dirty->bit_size, istate->cache_nr);
+
 	put_be32(&hdr_version, INDEX_EXTENSION_VERSION);
 	strbuf_add(sb, &hdr_version, sizeof(uint32_t));
 
@@ -236,6 +252,9 @@  void tweak_fsmonitor(struct index_state *istate)
 			}
 
 			/* Mark all previously saved entries as dirty */
+			if (istate->fsmonitor_dirty->bit_size > istate->cache_nr)
+				BUG("fsmonitor_dirty has more entries than the index (%"PRIuMAX" > %u)",
+				    (uintmax_t)istate->fsmonitor_dirty->bit_size, istate->cache_nr);
 			ewah_each_bit(istate->fsmonitor_dirty, fsmonitor_ewah_callback, istate);
 
 			/* Now mark the untracked cache for fsmonitor usage */
diff --git a/t/t7519-status-fsmonitor.sh b/t/t7519-status-fsmonitor.sh
index 81a375fa0f..87042470ab 100755
--- a/t/t7519-status-fsmonitor.sh
+++ b/t/t7519-status-fsmonitor.sh
@@ -354,4 +354,17 @@  test_expect_success 'discard_index() also discards fsmonitor info' '
 	test_cmp expect actual
 '
 
+# This test covers staging/unstaging files that appear at the end of the index.
+# Test files with names beginning with 'z' are used under the assumption that
+# earlier tests do not add/leave index entries that sort below them. 
+test_expect_success 'status succeeds after staging/unstaging ' '
+	test_commit initial &&
+	removed=$(test_seq 1 100 | sed "s/^/z/") &&
+	touch $removed &&
+	git add $removed &&
+	test_config core.fsmonitor "$TEST_DIRECTORY/t7519/fsmonitor-env" &&
+	FSMONITOR_LIST="$removed" git restore -S $removed &&
+	FSMONITOR_LIST="$removed" git status
+'
+
 test_done
diff --git a/t/t7519/fsmonitor-env b/t/t7519/fsmonitor-env
new file mode 100755
index 0000000000..8f1f7ab164
--- /dev/null
+++ b/t/t7519/fsmonitor-env
@@ -0,0 +1,24 @@ 
+#!/bin/sh
+#
+# An test hook script to integrate with git to test fsmonitor.
+#
+# The hook is passed a version (currently 1) and a time in nanoseconds
+# formatted as a string and outputs to stdout all files that have been
+# modified since the given time. Paths must be relative to the root of
+# the working tree and separated by a single NUL.
+#
+#echo "$0 $*" >&2
+
+if test "$#" -ne 2
+then
+	echo "$0: exactly 2 arguments expected" >&2
+	exit 2
+fi
+
+if test "$1" != 1
+then
+	echo "Unsupported core.fsmonitor hook version." >&2
+	exit 1
+fi
+
+printf '%s\n' $FSMONITOR_LIST