Re: [PATCH] bio allocation failure due to bio_get_nr_vecs()

[Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>]

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On 05/11/2012 04:06 PM, Jeff Moyer wrote:
> Bernd Schubert<bernd.schubert@itwm.fraunhofer.de>  writes:
>
>> diff --git a/fs/bio.c b/fs/bio.c
>> index e453924..84da885 100644
>> --- a/fs/bio.c
>> +++ b/fs/bio.c
>> @@ -505,9 +505,14 @@ EXPORT_SYMBOL(bio_clone);
>>   int bio_get_nr_vecs(struct block_device *bdev)
>>   {
>>   	struct request_queue *q = bdev_get_queue(bdev);
>> -	return min_t(unsigned,
>> +	int nr_pages;
>
> Looks like a corrupt patch.

What do you actually mean? Issue by thunderbird? I just saved the mail 
in my sent folder and it looks? Just to be sure, patch attached.


Thanks,
Bernd

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bio: bio_get_nr_vecs() must not return more than BIO_MAX_PAGES

From: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>

The number of bio_get_nr_vecs() is passed down via bio_alloc() to
bvec_alloc_bs(), which fails the bio allocation if
nr_iovecs > BIO_MAX_PAGES. For the underlying caller this causes an
unexpected bio allocation failure.
Limiting to queue_max_segments() is not sufficiet, as max_segments
also might be very large.

bvec_alloc_bs(gfp_mask, nr_iovecs, ) => NULL when nr_iovecs  > BIO_MAX_PAGES
bio_alloc_bioset(gfp_mask, nr_iovecs, ...)
bio_alloc(GFP_NOIO, nvecs)
xfs_alloc_ioend_bio()


Signed-off-by: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>
---
 fs/bio.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/bio.c b/fs/bio.c
index e453924..84da885 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -505,9 +505,14 @@ EXPORT_SYMBOL(bio_clone);
 int bio_get_nr_vecs(struct block_device *bdev)
 {
 	struct request_queue *q = bdev_get_queue(bdev);
-	return min_t(unsigned,
+	int nr_pages;
+
+	nr_pages = min_t(unsigned,
 		     queue_max_segments(q),
 		     queue_max_sectors(q) / (PAGE_SIZE >> 9) + 1);
+
+	return min_t(unsigned, nr_pages, BIO_MAX_PAGES);
+
 }
 EXPORT_SYMBOL(bio_get_nr_vecs);
 

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