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authorChristoph Lameter <clameter@sgi.com>2007-07-17 07:03:18 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-17 13:23:01 -0400
commit2492268472e7d326a6fe10f92f9211c4578f2482 (patch)
tree5f668469190b96bc0db13f836d774ae73cf385ca /Documentation
parent8e1f936b73150f5095448a0fee6d4f30a1f9001d (diff)
SLUB: change error reporting format to follow lockdep loosely
Changes the error reporting format to loosely follow lockdep. If data corruption is detected then we generate the following lines: ============================================ BUG <slab-cache>: <problem> -------------------------------------------- INFO: <more information> [possibly multiple times] <object dump> FIX <slab-cache>: <remedial action> This also adds some more intelligence to the data corruption detection. Its now capable of figuring out the start and end. Add a comment on how to configure SLUB so that a production system may continue to operate even though occasional slab corruption occur through a misbehaving kernel component. See "Emergency operations" in Documentation/vm/slub.txt. [akpm@linux-foundation.org: build fix] Signed-off-by: Christoph Lameter <clameter@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/vm/slub.txt137
1 files changed, 89 insertions, 48 deletions
diff --git a/Documentation/vm/slub.txt b/Documentation/vm/slub.txt
index df812b03b65d..d17f324db9f5 100644
--- a/Documentation/vm/slub.txt
+++ b/Documentation/vm/slub.txt
@@ -127,13 +127,20 @@ SLUB Debug output
127 127
128Here is a sample of slub debug output: 128Here is a sample of slub debug output:
129 129
130*** SLUB kmalloc-8: Redzone Active@0xc90f6d20 slab 0xc528c530 offset=3360 flags=0x400000c3 inuse=61 freelist=0xc90f6d58 130====================================================================
131 Bytes b4 0xc90f6d10: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ 131BUG kmalloc-8: Redzone overwritten
132 Object 0xc90f6d20: 31 30 31 39 2e 30 30 35 1019.005 132--------------------------------------------------------------------
133 Redzone 0xc90f6d28: 00 cc cc cc . 133
134FreePointer 0xc90f6d2c -> 0xc90f6d58 134INFO: 0xc90f6d28-0xc90f6d2b. First byte 0x00 instead of 0xcc
135Last alloc: get_modalias+0x61/0xf5 jiffies_ago=53 cpu=1 pid=554 135INFO: Slab 0xc528c530 flags=0x400000c3 inuse=61 fp=0xc90f6d58
136Filler 0xc90f6d50: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ 136INFO: Object 0xc90f6d20 @offset=3360 fp=0xc90f6d58
137INFO: Allocated in get_modalias+0x61/0xf5 age=53 cpu=1 pid=554
138
139Bytes b4 0xc90f6d10: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
140 Object 0xc90f6d20: 31 30 31 39 2e 30 30 35 1019.005
141 Redzone 0xc90f6d28: 00 cc cc cc .
142 Padding 0xc90f6d50: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
143
137 [<c010523d>] dump_trace+0x63/0x1eb 144 [<c010523d>] dump_trace+0x63/0x1eb
138 [<c01053df>] show_trace_log_lvl+0x1a/0x2f 145 [<c01053df>] show_trace_log_lvl+0x1a/0x2f
139 [<c010601d>] show_trace+0x12/0x14 146 [<c010601d>] show_trace+0x12/0x14
@@ -155,74 +162,108 @@ Filler 0xc90f6d50: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
155 [<c0104112>] sysenter_past_esp+0x5f/0x99 162 [<c0104112>] sysenter_past_esp+0x5f/0x99
156 [<b7f7b410>] 0xb7f7b410 163 [<b7f7b410>] 0xb7f7b410
157 ======================= 164 =======================
158@@@ SLUB kmalloc-8: Restoring redzone (0xcc) from 0xc90f6d28-0xc90f6d2b
159 165
166FIX kmalloc-8: Restoring Redzone 0xc90f6d28-0xc90f6d2b=0xcc
160 167
168If SLUB encounters a corrupted object (full detection requires the kernel
169to be booted with slub_debug) then the following output will be dumped
170into the syslog:
161 171
162If SLUB encounters a corrupted object then it will perform the following 1721. Description of the problem encountered
163actions:
164
1651. Isolation and report of the issue
166 173
167This will be a message in the system log starting with 174This will be a message in the system log starting with
168 175
169*** SLUB <slab cache affected>: <What went wrong>@<object address> 176===============================================
170offset=<offset of object into slab> flags=<slabflags> 177BUG <slab cache affected>: <What went wrong>
171inuse=<objects in use in this slab> freelist=<first free object in slab> 178-----------------------------------------------
172 179
1732. Report on how the problem was dealt with in order to ensure the continued 180INFO: <corruption start>-<corruption_end> <more info>
174operation of the system. 181INFO: Slab <address> <slab information>
182INFO: Object <address> <object information>
183INFO: Allocated in <kernel function> age=<jiffies since alloc> cpu=<allocated by
184 cpu> pid=<pid of the process>
185INFO: Freed in <kernel function> age=<jiffies since free> cpu=<freed by cpu>
186 pid=<pid of the process>
175 187
176These are messages in the system log beginning with 188(Object allocation / free information is only available if SLAB_STORE_USER is
177 189set for the slab. slub_debug sets that option)
178@@@ SLUB <slab cache affected>: <corrective action taken>
179 190
1912. The object contents if an object was involved.
180 192
181In the above sample SLUB found that the Redzone of an active object has 193Various types of lines can follow the BUG SLUB line:
182been overwritten. Here a string of 8 characters was written into a slab that
183has the length of 8 characters. However, a 8 character string needs a
184terminating 0. That zero has overwritten the first byte of the Redzone field.
185After reporting the details of the issue encountered the @@@ SLUB message
186tell us that SLUB has restored the redzone to its proper value and then
187system operations continue.
188
189Various types of lines can follow the @@@ SLUB line:
190 194
191Bytes b4 <address> : <bytes> 195Bytes b4 <address> : <bytes>
192 Show a few bytes before the object where the problem was detected. 196 Shows a few bytes before the object where the problem was detected.
193 Can be useful if the corruption does not stop with the start of the 197 Can be useful if the corruption does not stop with the start of the
194 object. 198 object.
195 199
196Object <address> : <bytes> 200Object <address> : <bytes>
197 The bytes of the object. If the object is inactive then the bytes 201 The bytes of the object. If the object is inactive then the bytes
198 typically contain poisoning values. Any non-poison value shows a 202 typically contain poison values. Any non-poison value shows a
199 corruption by a write after free. 203 corruption by a write after free.
200 204
201Redzone <address> : <bytes> 205Redzone <address> : <bytes>
202 The redzone following the object. The redzone is used to detect 206 The Redzone following the object. The Redzone is used to detect
203 writes after the object. All bytes should always have the same 207 writes after the object. All bytes should always have the same
204 value. If there is any deviation then it is due to a write after 208 value. If there is any deviation then it is due to a write after
205 the object boundary. 209 the object boundary.
206 210
207Freepointer 211 (Redzone information is only available if SLAB_RED_ZONE is set.
208 The pointer to the next free object in the slab. May become 212 slub_debug sets that option)
209 corrupted if overwriting continues after the red zone.
210
211Last alloc:
212Last free:
213 Shows the address from which the object was allocated/freed last.
214 We note the pid, the time and the CPU that did so. This is usually
215 the most useful information to figure out where things went wrong.
216 Here get_modalias() did an kmalloc(8) instead of a kmalloc(9).
217 213
218Filler <address> : <bytes> 214Padding <address> : <bytes>
219 Unused data to fill up the space in order to get the next object 215 Unused data to fill up the space in order to get the next object
220 properly aligned. In the debug case we make sure that there are 216 properly aligned. In the debug case we make sure that there are
221 at least 4 bytes of filler. This allow for the detection of writes 217 at least 4 bytes of padding. This allows the detection of writes
222 before the object. 218 before the object.
223 219
224Following the filler will be a stackdump. That stackdump describes the 2203. A stackdump
225location where the error was detected. The cause of the corruption is more 221
226likely to be found by looking at the information about the last alloc / free. 222The stackdump describes the location where the error was detected. The cause
223of the corruption is may be more likely found by looking at the function that
224allocated or freed the object.
225
2264. Report on how the problem was dealt with in order to ensure the continued
227operation of the system.
228
229These are messages in the system log beginning with
230
231FIX <slab cache affected>: <corrective action taken>
232
233In the above sample SLUB found that the Redzone of an active object has
234been overwritten. Here a string of 8 characters was written into a slab that
235has the length of 8 characters. However, a 8 character string needs a
236terminating 0. That zero has overwritten the first byte of the Redzone field.
237After reporting the details of the issue encountered the FIX SLUB message
238tell us that SLUB has restored the Redzone to its proper value and then
239system operations continue.
240
241Emergency operations:
242---------------------
243
244Minimal debugging (sanity checks alone) can be enabled by booting with
245
246 slub_debug=F
247
248This will be generally be enough to enable the resiliency features of slub
249which will keep the system running even if a bad kernel component will
250keep corrupting objects. This may be important for production systems.
251Performance will be impacted by the sanity checks and there will be a
252continual stream of error messages to the syslog but no additional memory
253will be used (unlike full debugging).
254
255No guarantees. The kernel component still needs to be fixed. Performance
256may be optimized further by locating the slab that experiences corruption
257and enabling debugging only for that cache
258
259I.e.
260
261 slub_debug=F,dentry
262
263If the corruption occurs by writing after the end of the object then it
264may be advisable to enable a Redzone to avoid corrupting the beginning
265of other objects.
266
267 slub_debug=FZ,dentry
227 268
228Christoph Lameter, <clameter@sgi.com>, May 23, 2007 269Christoph Lameter, <clameter@sgi.com>, May 30, 2007