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authorYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>2011-12-02 10:07:07 +0100
committerJens Axboe <axboe@kernel.dk>2011-12-02 10:07:07 +0100
commit5eb46851de3904cd1be9192fdacb8d34deadc1fc (patch)
treef0f0e6e6142cb50d8581477fb79a32f8f3a724ca /block
parent2984ff38ccf6cbc02a7a996a36c7d6f69f3c6146 (diff)
downloadlinux-5eb46851de3904cd1be9192fdacb8d34deadc1fc.tar.gz
cfq-iosched: fix cfq_cic_link() race confition
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 <isimatu.yasuaki@jp.fujitsu.com> Cc: stable@kernel.org Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/cfq-iosched.c11
1 files changed, 9 insertions, 2 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 3beed83437a..4c12869fcf7 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;
+retry:
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;
out: