path: root/block
diff options
authorYasuaki Ishimatsu <>2011-12-02 10:07:07 +0100
committerRohan Somvanshi <>2012-01-11 09:23:31 -0800
commit2be95e9bbff7680659d9a17f5d04d2c2c638edb9 (patch)
treed0786263af2ada3155fe299640bbf98d242a2145 /block
parent4b0dccaad0b0cc6148b8f2c61f9364f56c35f4fb (diff)
cfq-iosched: fix cfq_cic_link() race confition
commit 5eb46851de3904cd1be9192fdacb8d34deadc1fc upstream. cfq_cic_link() has race condition. When some processes which shared ioc issue I/O to same block device simultaneously, cfq_cic_link() returns -EEXIST sometimes. The race condition might stop I/O by following steps: step 1: Process A: Issue an I/O to /dev/sda step 2: Process A: Get an ioc (iocA here) in get_io_context() which does not linked with a cic for the device step 3: Process A: Get a new cic for the device (cicA here) in cfq_alloc_io_context() step 4: Process B: Issue an I/O to /dev/sda step 5: Process B: Get iocA in get_io_context() since process A and B share the same ioc step 6: Process B: Get a new cic for the device (cicB here) in cfq_alloc_io_context() since iocA has not been linked with a cic for the device yet step 7: Process A: Link cicA to iocA in cfq_cic_link() step 8: Process A: Dispatch I/O to driver and finish it step 9: Process B: Try to link cicB to iocA in cfq_cic_link() But it fails with showing "cfq: cic link failed!" kernel message, since iocA has already linked with cicA at step 7. step 10: Process B: Wait for finishig I/O in get_request_wait() The function does not wake up, when there is no I/O to the device. When cfq_cic_link() returns -EEXIST, it means ioc has already linked with cic. So when cfq_cic_link() return -EEXIST, retry cfq_cic_lookup(). Signed-off-by: Yasuaki Ishimatsu <> Signed-off-by: Jens Axboe <> Signed-off-by: Greg Kroah-Hartman <> Change-Id: I679b98b517dcddd7c3568081b50948a786884ad1 Reviewed-on: http://git-master/r/74162 Reviewed-by: Varun Wadekar <> Tested-by: Varun Wadekar <>
Diffstat (limited to 'block')
1 files changed, 9 insertions, 2 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 3beed83437a3..4c12869fcf77 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3184,7 +3184,7 @@ static int cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
- if (ret)
+ if (ret && ret != -EEXIST)
printk(KERN_ERR "cfq: cic link failed!\n");
return ret;
@@ -3200,6 +3200,7 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
struct io_context *ioc = NULL;
struct cfq_io_context *cic;
+ int ret;
might_sleep_if(gfp_mask & __GFP_WAIT);
@@ -3207,6 +3208,7 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
if (!ioc)
return NULL;
cic = cfq_cic_lookup(cfqd, ioc);
if (cic)
goto out;
@@ -3215,7 +3217,12 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
if (cic == NULL)
goto err;
- if (cfq_cic_link(cfqd, ioc, cic, gfp_mask))
+ ret = cfq_cic_link(cfqd, ioc, cic, gfp_mask);
+ if (ret == -EEXIST) {
+ /* someone has linked cic to ioc already */
+ cfq_cic_free(cic);
+ goto retry;
+ } else if (ret)
goto err_free;