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| author | Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> | 2011-12-02 10:07:07 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2011-12-02 10:07:07 +0100 |
| commit | 5eb46851de3904cd1be9192fdacb8d34deadc1fc (patch) | |
| tree | f0f0e6e6142cb50d8581477fb79a32f8f3a724ca /block | |
| parent | 2984ff38ccf6cbc02a7a996a36c7d6f69f3c6146 (diff) | |
| download | lwn-5eb46851de3904cd1be9192fdacb8d34deadc1fc.tar.gz lwn-5eb46851de3904cd1be9192fdacb8d34deadc1fc.zip | |
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.c | 11 |
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; +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: |