Attachment 695035 Details for Bug 831158 – Proposed patch

[patch] Proposed patch

0001-dm-crypt-fix-mempool-deadlock.patch (text/plain), 2.44 KB, created by Milan Broz on 2013-02-08 12:08:10 UTC

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Creator: Milan Broz

Created: 2013-02-08 12:08:10 UTC

Size: 2.44 KB

patch

obsolete

>From 6b97c677d5c3bf518d95110088ce9cc6b5b98509 Mon Sep 17 00:00:00 2001
>From: Milan Broz <mbroz@redhat.com>
>Date: Thu, 2 Aug 2012 15:54:17 +0200
>Subject: [RHEL6.4 PATCH] dm crypt: fix mempool deadlock
>
>dm crypt: fix possible mempool deadlock
>Resolves: 831158
>
>There is no reproducer but kernel with patch tested using
>intensive performance tests + cryptsetup testsuite.
>
>Backport of upstream commit
>commit aeb2deae2660a1773c83d3c6e9e6575daa3855d6
>Author: Mikulas Patocka <mpatocka@redhat.com>
>
>This patch fixes a possible deadlock in dm-crypt's mempool use.
>
>Currently, dm-crypt reserves a mempool of MIN_BIO_PAGES reserved pages.
>It allocates first MIN_BIO_PAGES with non-failing allocation (the allocation
>cannot fail and waits until the mempool is refilled). Further pages are
>allocated with different gfp flags that allow failing.
>
>Because allocations may be done in parallel, this code can deadlock. Example:
>There are two processes, each tries to allocate MIN_BIO_PAGES and the processes
>run simultaneously.
>It may end up in a situation where each process allocates (MIN_BIO_PAGES / 2)
>pages. The mempool is exhausted. Each process waits for more pages to be freed
>to the mempool, which never happens.
>
>To avoid this deadlock scenario, this patch changes the code so that only
>the first page is allocated with non-failing gfp mask. Allocation of further
>pages may fail.
>---
> drivers/md/dm-crypt.c |   10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
>index 82b9fe3..957c08f 100644
>--- a/drivers/md/dm-crypt.c
>+++ b/drivers/md/dm-crypt.c
>@@ -141,7 +141,6 @@ struct crypt_config {
> 
> #define MIN_IOS        16
> #define MIN_POOL_PAGES 32
>-#define MIN_BIO_PAGES  8
> 
> static struct kmem_cache *_crypt_io_pool;
> 
>@@ -551,12 +550,11 @@ static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned size,
> 		}
> 
> 		/*
>-		 * if additional pages cannot be allocated without waiting,
>-		 * return a partially allocated bio, the caller will then try
>-		 * to allocate additional bios while submitting this partial bio
>+		 * If additional pages cannot be allocated without waiting,
>+		 * return a partially-allocated bio.  The caller will then try
>+		 * to allocate more bios while submitting this partial bio.
> 		 */
>-		if (i == (MIN_BIO_PAGES - 1))
>-			gfp_mask = (gfp_mask | __GFP_NOWARN) & ~__GFP_WAIT;
>+		gfp_mask = (gfp_mask | __GFP_NOWARN) & ~__GFP_WAIT;
> 
> 		len = (size > PAGE_SIZE) ? PAGE_SIZE : size;
> 
>-- 
>1.7.10.4
>

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Attachments on bug 831158: 695035