Expand upon a comment in os_unix.c. No changes to code.

FossilOrigin-Name: 77933dc4dbe0e0af3b13a14293a8bd684edc5056f4ae9291c6f95d4433bf90ce

manifest

@@ -1,5 +1,5 @@
-C In\sthe\sjson\soutput\smode\sof\sthe\sCLI,\sdo\scorrect\squoting\sof\sescape\scharacters.\nAlso,\sshow\sBLOBs\sas\sJSON\sstrings,\spossibly\swith\sembedded\s\\u0000\sbytes.
-D 2020-05-29T00:21:43.757
+C Expand\supon\sa\scomment\sin\sos_unix.c.\sNo\schanges\sto\scode.
+D 2020-05-29T11:07:20.452
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 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -517,7 +517,7 @@ F src/os.c 669cc3839cc35d20f81faf0be1ab6d4581cea35e9d8f3a9d48a98d6571f7c285
 F src/os.h 48388821692e87da174ea198bf96b1b2d9d83be5dfc908f673ee21fafbe0d432
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
-F src/os_unix.c 13f983da988b6460ef3c4c22099c67ab0938291e543644ac4d99eccc8ba604f1
+F src/os_unix.c 03bad4eb1e13946cb967f3a6cc0a0d350df8ea4b8d2212d528024a5f9abc90ea
 F src/os_win.c e832e21e830c1f9409c9c54053939b6dcb14c1e92128b756204ce1e3e331d678
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 F src/pager.c 96436cb1920074d4ade120a1a8a9d0ae3f52df06651e21b7eccc5eae2f02b111
@@ -1866,7 +1866,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
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-U drh
-Z 9c1cf56bec8bac52da07f5875b8a7be2
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+U dan
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manifest.uuid

@@ -1 +1 @@
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+77933dc4dbe0e0af3b13a14293a8bd684edc5056f4ae9291c6f95d4433bf90ce

src/os_unix.c

@@ -4836,7 +4836,10 @@ static int unixShmLock(
   **
   ** In other words, if this is a blocking lock, none of the locks that
   ** occur later in the above list than the lock being obtained may be
-  ** held.  */
+  ** held.  
+  **
+  ** It is not permitted to block on the RECOVER lock.
+  */
 #ifdef SQLITE_ENABLE_SETLK_TIMEOUT
   assert( (flags & SQLITE_SHM_UNLOCK) || pDbFd->iBusyTimeout==0 || (
          (ofst!=2)                                   /* not RECOVER */