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authorJan Kara <jack@suse.cz>2009-04-13 14:40:14 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-13 15:04:33 -0700
commit316cb4ef3eb2ad6e35e15cc56d39c6cda58c093a (patch)
tree23084bf762a3dc0ec91c299c5f10206b132df621 /drivers/atm/solos-pci.c
parentcaefba1740d8016e6dfe8fda84f85bdcb8f8c85d (diff)
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ext2: fix data corruption for racing writes
If two writers allocating blocks to file race with each other (e.g. because writepages races with ordinary write or two writepages race with each other), ext2_getblock() can be called on the same inode in parallel. Before we are going to allocate new blocks, we have to recheck the block chain we have obtained so far without holding truncate_mutex. Otherwise we could overwrite the indirect block pointer set by the other writer leading to data loss. The below test program by Ying is able to reproduce the data loss with ext2 on in BRD in a few minutes if the machine is under memory pressure: long kMemSize = 50 << 20; int kPageSize = 4096; int main(int argc, char **argv) { int status; int count = 0; int i; char *fname = "/mnt/test.mmap"; char *mem; unlink(fname); int fd = open(fname, O_CREAT | O_EXCL | O_RDWR, 0600); status = ftruncate(fd, kMemSize); mem = mmap(0, kMemSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); // Fill the memory with 1s. memset(mem, 1, kMemSize); sleep(2); for (i = 0; i < kMemSize; i++) { int byte_good = mem[i] != 0; if (!byte_good && ((i % kPageSize) == 0)) { //printf("%d ", i / kPageSize); count++; } } munmap(mem, kMemSize); close(fd); unlink(fname); if (count > 0) { printf("Running %d bad page\n", count); return 1; } return 0; } Cc: Ying Han <yinghan@google.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Jan Kara <jack@suse.cz> Cc: Mingming Cao <cmm@us.ibm.com> Cc: <linux-ext4@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/atm/solos-pci.c')
0 files changed, 0 insertions, 0 deletions