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H A D | dm-crypt.c | 610f2de3 Thu Feb 20 17:01:01 CST 2014 Mikulas Patocka <mpatocka@redhat.com> dm crypt: fix cpu hotplug crash by removing per-cpu structure
The DM crypt target used per-cpu structures to hold pointers to a ablkcipher_request structure. The code assumed that the work item keeps executing on a single CPU, so it didn't use synchronization when accessing this structure.
If a CPU is disabled by writing 0 to /sys/devices/system/cpu/cpu*/online, the work item could be moved to another CPU. This causes dm-crypt crashes, like the following, because the code starts using an incorrect ablkcipher_request:
smpboot: CPU 7 is now offline BUG: unable to handle kernel NULL pointer dereference at 0000000000000130 IP: [<ffffffffa1862b3d>] crypt_convert+0x12d/0x3c0 [dm_crypt] ... Call Trace: [<ffffffffa1864415>] ? kcryptd_crypt+0x305/0x470 [dm_crypt] [<ffffffff81062060>] ? finish_task_switch+0x40/0xc0 [<ffffffff81052a28>] ? process_one_work+0x168/0x470 [<ffffffff8105366b>] ? worker_thread+0x10b/0x390 [<ffffffff81053560>] ? manage_workers.isra.26+0x290/0x290 [<ffffffff81058d9f>] ? kthread+0xaf/0xc0 [<ffffffff81058cf0>] ? kthread_create_on_node+0x120/0x120 [<ffffffff813464ac>] ? ret_from_fork+0x7c/0xb0 [<ffffffff81058cf0>] ? kthread_create_on_node+0x120/0x120
Fix this bug by removing the per-cpu definition. The structure ablkcipher_request is accessed via a pointer from convert_context. Consequently, if the work item is rescheduled to a different CPU, the thread still uses the same ablkcipher_request.
This change may undermine performance improvements intended by commit c0297721 ("dm crypt: scale to multiple cpus") on select hardware. In practice no performance difference was observed on recent hardware. But regardless, correctness is more important than performance.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Cc: stable@vger.kernel.org c0297721 Thu Jan 13 13:59:53 CST 2011 Andi Kleen <ak@linux.intel.com> dm crypt: scale to multiple cpus
Currently dm-crypt does all the encryption work for a single dm-crypt mapping in a single workqueue. This does not scale well when multiple CPUs are submitting IO at a high rate. The single CPU running the single thread cannot keep up with the encryption and encrypted IO performance tanks.
This patch changes the crypto workqueue to be per CPU. This means that as long as the IO submitter (or the interrupt target CPUs for reads) runs on different CPUs the encryption work will be also parallel.
To avoid a bottleneck on the IO worker I also changed those to be per-CPU threads.
There is still some shared data, so I suspect some bouncing cache lines. But I haven't done a detailed study on that yet.
Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Milan Broz <mbroz@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> 610f2de3 Thu Feb 20 17:01:01 CST 2014 Mikulas Patocka <mpatocka@redhat.com> dm crypt: fix cpu hotplug crash by removing per-cpu structure The DM crypt target used per-cpu structures to hold pointers to a ablkcipher_request structure. The code assumed that the work item keeps executing on a single CPU, so it didn't use synchronization when accessing this structure. If a CPU is disabled by writing 0 to /sys/devices/system/cpu/cpu*/online, the work item could be moved to another CPU. This causes dm-crypt crashes, like the following, because the code starts using an incorrect ablkcipher_request: smpboot: CPU 7 is now offline BUG: unable to handle kernel NULL pointer dereference at 0000000000000130 IP: [<ffffffffa1862b3d>] crypt_convert+0x12d/0x3c0 [dm_crypt] ... Call Trace: [<ffffffffa1864415>] ? kcryptd_crypt+0x305/0x470 [dm_crypt] [<ffffffff81062060>] ? finish_task_switch+0x40/0xc0 [<ffffffff81052a28>] ? process_one_work+0x168/0x470 [<ffffffff8105366b>] ? worker_thread+0x10b/0x390 [<ffffffff81053560>] ? manage_workers.isra.26+0x290/0x290 [<ffffffff81058d9f>] ? kthread+0xaf/0xc0 [<ffffffff81058cf0>] ? kthread_create_on_node+0x120/0x120 [<ffffffff813464ac>] ? ret_from_fork+0x7c/0xb0 [<ffffffff81058cf0>] ? kthread_create_on_node+0x120/0x120 Fix this bug by removing the per-cpu definition. The structure ablkcipher_request is accessed via a pointer from convert_context. Consequently, if the work item is rescheduled to a different CPU, the thread still uses the same ablkcipher_request. This change may undermine performance improvements intended by commit c0297721 ("dm crypt: scale to multiple cpus") on select hardware. In practice no performance difference was observed on recent hardware. But regardless, correctness is more important than performance. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Cc: stable@vger.kernel.org c0297721 Thu Jan 13 13:59:53 CST 2011 Andi Kleen <ak@linux.intel.com> dm crypt: scale to multiple cpus Currently dm-crypt does all the encryption work for a single dm-crypt mapping in a single workqueue. This does not scale well when multiple CPUs are submitting IO at a high rate. The single CPU running the single thread cannot keep up with the encryption and encrypted IO performance tanks. This patch changes the crypto workqueue to be per CPU. This means that as long as the IO submitter (or the interrupt target CPUs for reads) runs on different CPUs the encryption work will be also parallel. To avoid a bottleneck on the IO worker I also changed those to be per-CPU threads. There is still some shared data, so I suspect some bouncing cache lines. But I haven't done a detailed study on that yet. Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Milan Broz <mbroz@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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