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Re: [PATCH] read-cache: fix division by zero core-dump






On 9/27/2018 6:24 PM, Ramsay Jones wrote:

commit 225df8a468 ("ieot: add Index Entry Offset Table (IEOT)
extension", 2018-09-26) added a 'DIV_ROUND_UP(entries, ieot_blocks)
expression, where ieot_blocks was set to zero for a single cpu
platform. This caused an SIGFPE and a core dump in practically
every test in the test-suite, until test t4056-diff-order.sh, which
then went into an infinite loop!

Signed-off-by: Ramsay Jones <ramsay@xxxxxxxxxxxxxxxxxxxx>
---

Hi Ben,

Could you please squash this into the relevant commits on your
'bp/read-cache-parallel' branch. (The first hunk fixes a sparse
warning about using an integer as a NULL pointer).


Absolutely - thanks for the patch.

I don't know how long it's been since I've been on a single core CPU - I'm sad for you. ;-)

Thanks!

ATB,
Ramsay Jones

  read-cache.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/read-cache.c b/read-cache.c
index 6755d58877..40f096f70a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2141,7 +2141,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
  	size_t extension_offset = 0;
  #ifndef NO_PTHREADS
  	int nr_threads, cpus;
-	struct index_entry_offset_table *ieot = 0;
+	struct index_entry_offset_table *ieot = NULL;
  #endif
if (istate->initialized)
@@ -2771,7 +2771,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
  			if (ieot_blocks < 1)
  				ieot_blocks = 1;
  			cpus = online_cpus();
-			if (ieot_blocks > cpus - 1)
+			if (cpus > 1 && ieot_blocks > cpus - 1)
  				ieot_blocks = cpus - 1;
  		} else {
  			ieot_blocks = nr;