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authorYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>2011-12-02 04:07:07 -0500
committerJens Axboe <axboe@kernel.dk>2011-12-02 04:07:07 -0500
commit5eb46851de3904cd1be9192fdacb8d34deadc1fc (patch)
treef0f0e6e6142cb50d8581477fb79a32f8f3a724ca /block/cfq-iosched.c
parent2984ff38ccf6cbc02a7a996a36c7d6f69f3c6146 (diff)
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/cfq-iosched.c')
-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 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,
3184 } 3184 }
3185 } 3185 }
3186 3186
3187 if (ret) 3187 if (ret && ret != -EEXIST)
3188 printk(KERN_ERR "cfq: cic link failed!\n"); 3188 printk(KERN_ERR "cfq: cic link failed!\n");
3189 3189
3190 return ret; 3190 return ret;
@@ -3200,6 +3200,7 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
3200{ 3200{
3201 struct io_context *ioc = NULL; 3201 struct io_context *ioc = NULL;
3202 struct cfq_io_context *cic; 3202 struct cfq_io_context *cic;
3203 int ret;
3203 3204
3204 might_sleep_if(gfp_mask & __GFP_WAIT); 3205 might_sleep_if(gfp_mask & __GFP_WAIT);
3205 3206
@@ -3207,6 +3208,7 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
3207 if (!ioc) 3208 if (!ioc)
3208 return NULL; 3209 return NULL;
3209 3210
3211retry:
3210 cic = cfq_cic_lookup(cfqd, ioc); 3212 cic = cfq_cic_lookup(cfqd, ioc);
3211 if (cic) 3213 if (cic)
3212 goto out; 3214 goto out;
@@ -3215,7 +3217,12 @@ cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
3215 if (cic == NULL) 3217 if (cic == NULL)
3216 goto err; 3218 goto err;
3217 3219
3218 if (cfq_cic_link(cfqd, ioc, cic, gfp_mask)) 3220 ret = cfq_cic_link(cfqd, ioc, cic, gfp_mask);
3221 if (ret == -EEXIST) {
3222 /* someone has linked cic to ioc already */
3223 cfq_cic_free(cic);
3224 goto retry;
3225 } else if (ret)
3219 goto err_free; 3226 goto err_free;
3220 3227
3221out: 3228out: