Re: [BUG] Core dump w/ bus error on bad mmap'd packfile
Amit Bakshi ambak...@gmail.com writes: I was getting core dumps (bus error 7) with git 1.7.1 when doing a git checkout. I tried git fsck, and same thing. I got the same with precompiled rpms of 1.7.12, and with a locally compiled version of git 1.8.5. [...] $ git fsck Checking pack-0ccb5ee4f60003a7ea47d6904633cce5973efa60.pack in: 0x7f9070507000 remain: 17345210 offset: 17345230 Bus error (core dumped) git verify-pack correctly shows the error, without a bus error. $ git verify-pack -v pack-0ccb5ee4f60003a7ea47d6904633cce5973efa60.pack fatal: read error on input: Input/output error pack-0ccb5ee4f60003a7ea47d6904633cce5973efa60.pack: bad mmap()ing a file and attempting to read from parts that the kernel can then not page in (in your case because it couldn't read the file) are expected to give a SIGBUS, so there is no bug here. The different behavior comes from some commands using mmap() and some using read() to access the packs. Perhaps we could try to map the faulting address back to the file it came from, though. The siginfo_t for a SIGBUS contains information about the faulting address, so for the case of packs we could walk the 'struct packed_git' list and see which open window the address belongs to. I need to think about the implications of doing that in a signal handler, though. -- Thomas Rast t...@thomasrast.ch -- To unsubscribe from this list: send the line unsubscribe git in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[BUG] Core dump w/ bus error on bad mmap'd packfile
Hi, I was getting core dumps (bus error 7) with git 1.7.1 when doing a git checkout. I tried git fsck, and same thing. I got the same with precompiled rpms of 1.7.12, and with a locally compiled version of git 1.8.5. The simplest/quickest repro I got is using git-fsck. The stacktrace blames SHA1_Update in verify_packfile. Upon further investigation all the in/offsets/remaining seemed ok. I traced it to a 17mb packfile that gets an i/o error when attempting to read it past 13mb. It looks like it's xmmap'ing the file and passing that pointer to SHA1_Update(). I don't know why in some paths it gives an i/o error and in other paths it segfaults (I added the extra debug output to git-fsck). $ git fsck Checking pack-0ccb5ee4f60003a7ea47d6904633cce5973efa60.pack in: 0x7f9070507000 remain: 17345210 offset: 17345230 Bus error (core dumped) git verify-pack correctly shows the error, without a bus error. $ git verify-pack -v pack-0ccb5ee4f60003a7ea47d6904633cce5973efa60.pack fatal: read error on input: Input/output error pack-0ccb5ee4f60003a7ea47d6904633cce5973efa60.pack: bad Not sure what the right solution is without impacting perf, but it took me a while to track down and having an error message indicating the bad file would've been a great help. Amit -- To unsubscribe from this list: send the line unsubscribe git in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
