diff options
| author | Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> | 2011-12-02 10:07:07 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2012-01-06 14:13:46 -0800 |
| commit | cec3c159f674367def095745a72ac6150f889243 (patch) | |
| tree | 3fefce578c3ede09ef02d3a241b0e29cf2fc5a17 | |
| parent | 8f8a594251e5260f53d746887890d0d2185ceebb (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 <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
| -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 aae94473b581..23500ac7f0f3 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -3169,7 +3169,7 @@ 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; @@ -3185,6 +3185,7 @@ 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); @@ -3192,6 +3193,7 @@ 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; @@ -3200,7 +3202,12 @@ 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: |